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COIMK 


s 

CONNECTICUT  ^fj 

Agricultural  Experiment  Station 


NEW  HAVEN,  CONN. 


BULLETIN  239  MAY,  1922 


WILDFIRE  OF  TOBACCO  IN 
CONNECTICUT 

Bv  GEORGE  P.  CLINTON  and   FLORENCE  A.   McCORMICK 


CONTENTS 

Introduction  365 

Distribution    366 

Possible  Methods  of  Introduction 369 

Agents  of  Dispersal 372 

Overwintering  of  the  Germs 375 

Detailed  Distribution  in  the  State  377 

Disease  in  the  Seedbeds  .' 380 

Disease  in  the  Fields  387 

Seedbed  and  Field  Experiments  398 

Laboratory  Studies 411 

Recommendations  for  Control   421 

Literature    422 


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CONNECTICUT   AGRICULTURAL   EXPERIMENT   STATION 

OFFICERS  AND  STAFF 

May,  1922 


BOARD  OF  CONTROL. 
His  Excellency,  Everett  J.  Lake,  ex-officio,  President. 

James  H.  Webb,  Vice  President Hamden 

George  A.  Hopson,  Secretary Mt.  Carmel 

E.  H.  Jenkins,  Director  and  Treasurer New  Haven 

Joseph  W.  Alsop  Avon 

Charles  R.  Treat   Orange 

Elijah  Rogers : Southington 

Edward  C.  Schneider  Middletown 

STAFF. 

Administration.  E.  H.  Jenkins,  Ph.D.,  Director  and  Treasurer. 

Miss  V.  E.  Cole,  Librarian  and  Stenographer. 

Miss  L.  M.  Brautlecht,  Bookkeeper  and  Stenographer. 

Miss  J.  V.  Berger,  Stenographer. 

William  Veitch,  In  charge  of  Buildings  and  Grounds. 

Chemistry: 

Analytical  Laboratory.  E.  Monroe  Bailey,  Ph.D.,  Chemist  in  Charge. 

R.  E.  Andrew,  M.A.  \ 

C.  E.   Shepard,  [  •         .  _, 

„  T     -v,  „  -,,  r  Assistant  Chemists. 

Owen  L.  Nolan,     Richard  Merwin,    I 

Harry  J.  Fisher,  B.A.  ,' 

Frank  Sheldon,  Laboratory  Assistant. 

V.  L.  Churchill,  Sampling  Agent. 

Miss  Alta  H.  Moss,  Clerk. 

Biochemical 

Laboratory.  T.  B.  Osborne,  Ph.D.,  Sc.D.,  Chemist  in  Charge. 

Botany.  G.  P.  Clinton,  Sc.D.,  Botanist  in  Charge. 

E.  M.  Stoddard,  B.S.,  Pomologist. 
Miss  Florence  A.  McCormick,  Ph.D.,  Pathologist. 
G.  E.  Graham,  Assistant. 
Mrs.  W.  W.  Kelsey,  Secretary. 

Entomology.  W.   E.   Britton,  Ph.D.,  Entomologist  in   Charge;    State  Ento- 

mologist. 
B.  H.  Walden,  B.Agr.,  M.  P.  Zappe,  B.S.,    )  Assistant 
Philip  Garman,  Ph.D.  \     Entomologists. 

John  T.  Ashworth,  Deputy  in  Charge  of  Gipsy  Moth  Work. 
Samuel  T.  Sealy,  Deputy  in  Charge  of  Mosquito  Control. 
Miss  Gladys  M.  Finley,  Stenographer. 

Forestry.  Walter  O.  Filley,  Forester  in  Charge. 

A.  E.  Moss,  M.F.,  Assistant. 
H.  W.  Hicock,  M.F.,  Assistant. 
Miss  Pauline  A.  Merchant,  Stenographer. 

Plant  Breeding.  Donald  F.  Jones,  S.D.,  Plant  Breeder  in  Charge. 

P.  C  Mangelsdorf,  B.S.,  Assistant. 
In  charge  of  the 

Tobacco  Station.  G.  H.  Chapman,  Ph.D.,  Windsor,  Conn. 


WILDFIRE  OF  TOBACCO  IN  CONNECTICUT. 

George  P.  Clinton  and  Florence  A.  McCormick. 

Introduction. 

State  Survey.  The  question  of  establishing-  a  sub-station  for 
tobacco  experimentation  having'  been  presented  to  the  Director  of 
the  New  Haven  Station  early  in  1920  by  County  Agent  B.  G. 
Southwick  of  Hartford  County,  it  was  decided  that  before  any 
definite  decision  was  given  there  should  be  made  some  preliminary 
investigations.  These  were  to  include  a  canvass  of  the  opinions  of 
tobacco  growers  toward  such  a  proposition  and  a  survey  of  the 
tobacco  districts,  to  determine  the  diseases  and  injuries  with  which 
the  growers  had  to  contend.  In  1920  this  survey  was  undertaken 
by  the  joint  financial  cooperation  of  the  Experiment  Station,  the 
Hartford  County  Farm  Bureau  and  the  Extension  Service  of  the 
Connecticut  Agricultural  College.  Somewhat  similar  work  was 
undertaken  by  the  Massachusetts  Station  in  that  state.  In  Con- 
necticut the  work  resolved  itself  largely  into  a  disease  survey  of 
tobacco  seedbeds  and  fields,  for  which  Mr.  Southwick  served  as  a 
scout,  in  connection  with  his  interviews  with  the  growers,  and  the 
writers  as  the  botanical  investigators  of  the  troubles  brought  to 
light. 

After  the  preliminary  work  of  seedbed  examinations  by  Mr. 
Southwick  and  Dr.  Clinton  in  May  and  June,  it  was  decided  to 
facilitate  the  field  work  by  establishing,  during  July  and  August,  a 
small  laboratory  at  the  Farm  Bureau  headquarters  in  Hartford 
with  Dr.  McCormick  in  charge,  Dr.  Clinton  being  in  Europe. 
During  the  entire  season  of  1921  the  work  was  continued  with  even 
more  intensity.  No  field  laboratory  was  maintained  this  year  at 
Hartford,  the  work  being  done  at  New  Haven,  but  considerable 
experimental  work  was  carried  on  at  the  Station's  new  tobacco 
farm  at  Windsor,  the  state  by  that  time  having  authorized  by  law 
tobacco  investigations  for  which  an  appropriation  was  given.  Mr. 
G.  E.  Graham,  assistant  in  the  botanical  department  of  the  Experi- 
ment Station,  helped  with  the  various  experiments  there  and  else- 
where in  1 92 1. 

In  the  disease  survey  considerable  data  were  obtained,  much  of 
which,  however,  was  merely  an  extension  of  the  knowledge  of 
diseases  and  injuries  that  had  been  previously  studied  more  or  less 
intensively  by  the  Station  botanist.  It  is  hoped  to  present  this  and 
further  data  in  future  bulletins  from  this  department.  One  of  the 
striking  features  of  the  survey  was  the  discovery  of  a  tobacco 
disease,  new  to  the  state,  which  has  now  proved  to  be  quite  serious 
under  certain  conditions.  It  is  with  this  trouble,  popularly  known 
as  wildfire,  that  this  bulletin  has  to  deal. 


366         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Nature  of  the  Disease.  As  a  result  of  one  of  the  field  examina- 
tions in  late  June,  1920,  Mr.  Southwick  sent  to  New  Haven  plants 
from  Tariffville  showing  an  unusual  leaf  spot  trouble,  but  no  defi- 
nite information  concerning  it  was  obtained  at  that  time  because 
of  the  poor  condition  of  the  material  when  received.  Later  zt 
Hartford  Dr.  McCormick,  in  examinations  of  other  material 
brought  to  the  laboratory  by  a  grower  from  Poquonock,  found 
the  diseased  spots  accompanied  by  bacteria  with  which  she  was 
able  to  produce  infection  on  healthy  plants. 

The  subsequent  studies  of  the  disease  by  the  writers  have  been 
made,  ist,  to  thoroughly  convince  'themselves  of  its  bacterial 
nature,  since  some  growers  have  been  very  sceptical  as  to  its  iden- 
tity and  the  damage  it  might  cause,  and  2d,  to  find  practical 
methods  for  its  control,  since,  in  1920  and  even  more  so  in  1921, 
it  proved  a  serious  trouble  in  certain  localities  and  fields. 

General  Description.  The  disease  is  generally  limited  to  the 
leaves,  and  under  certain  conditions  does  not  prove  serious,  but 
with  the  right  weather  conditions  its  possibilities  of  injury  are 
unusually  great.  It  belongs  with  the  leaf  spot  troubles  of  which 
several  have  been  found  in  this  state.  It  differs,  however,  from 
all  the  other  leaf  spots  by  certain  definite  characters,  usually 
evident  to  the  ordinary  observer.  In  both  the  seedbed  and  field, 
infected  plants  develop  yellow  discolorations  in  the  normally  green 
tissues  and  these  spots  are  usually  rounded  and  about  the  size  of 
a  finger  tip.  In  their  center  there  is  a  small  point  of  white  to 
brownish  dead  tissue  that  indicates  the  origin  of  the  spot.  In  time 
the  dead  center  encroaches  on  the  yellow  discoloration  limiting  it 
to  a  more  or  less  narrow  encircling  band,  the  so-called  halo.  If 
numerous  enough  the  spots  cause  death  of  intervening  tissues  so 
that  eventually  a  very  large  part  of  the  leaf  surface  is  killed  in  an 
irregular  way  as  if  by  sun  scorch.  The  appearance  then  is  much 
like  the  so-called  rust  that  follows  calico,  but  usually  even  at  this 
late  stage  the  yellow  halo  rings  are  still  evident  for  definite  iden- 
tification. 

Distribution. 

In  Other  Countries.  Because  the  blue  mold,  a  menace  to 
tobacco  in  certain  parts  of  Asia  and  Australia,  has  recently 
appeared  in  this  country,  some  persons  have  thought  that  wildfire 
has  been  imported  from  similar  tobacco  districts  into  the  United 
States.  Wolf  and  Moss  (33,  p.  25.)  in  1919  stated  that  "it  is 
presumably  identical  with  a  disease  which  has  been  recently 
reported  from  Connecticut  and  from  the  Philippine  Islands."  So 
far  as  Connecticut  is  concerned  their  statement  was  correct.  The 
disease  mentioned  from  the  Philippine  Islands  is  evidently  that 
briefly  described  by  Reinking  (22,  p.  130.)  also  in  1919.  It  is 
impossible  to  tell  definitely  from  Reinking's  preliminary  descrip- 


DISTRIBUTION.  367 

tion  whether  or  not  he  is  dealing  with  the  wildfire  or  some  of  the 
other  bacterial  spots  now  known  on  tobacco. 

Very  recently  Fromme  (7,  p.  37.)  called  attention  to  a  disease 
in  Africa  which  is  described  (evidently  by  the  editor  Klerck,  19.) 
in  the  Journal  of  the  Department  of  Agriculture,  Union  of  South 
Africa,  in  March,  1921,  as  follows: 

"A  tobacco  disease  occurring  in  the  Piet-Retief  District  and  known  to 
farmers  as  'Verterende  roest,'  was  brought  to  our  notice  by  the  Chief  of  the 
Tobacco  and  Cotton  Division.  An  officer  of  this  Division  was  detailed  to 
investigate  the  matter ;  the  disease  starts  on  the  lower  leaves  which  at  first 
appear  to  be  maturing  prematurely,  and  spreads  to  the  upper  leaves.  The 
disease  was  prevalent  on  the  experiment  station  as  well  as  on  neighboring 
farms,  and  it  was  stated  that  only  10  per  cent,  of  the  1920  crop  reached  its 
normal  development,  the  remaining  plants  being  stunted.  Considerable 
losses  had  also  been  suffered  on  other  farms  which  were  visited.  The 
'verterende  roest'  is  due  to  a  bacterium  which  is  being  carefully  studied  in 
the  laboratory,  with  a  view  to  devising  preventive  measures  which  may  be 
tested  on  a  practical  scale  next  season.  Specimens  of  the  tobacco  affected 
by  a  similar  trouble  have  also  been  received  from  Rhodesia ;  these  are  also 
under  investigation."  A  month  later  he  further  states  "The  bacterial 
disease  of  tobacco  previously  recorded  from  the  Piet-Retief  District  is  now 
spreading  rapidly  at  Marikana  in  the  Rustenburg  District,  and  is  probably 
very  widespread.  So  far  as  this  investigation  of  this  disease  has  gone,  it 
bears  a  very  strong  resemblance  to  the  wildfire  in  tobacco  recorded  in  the 
United  States." 

In  the  same  publication.  Evans  (34)  in  January,  1922,  makes  the 
following  definite  statement : 

"Tobacco  Wild  Fire  (Bacterium  tabacum),  a  serious  disease,  was  investi- 
gated. It  occurs  extensively  in  the  Pietersburg  and  Rustenburg  Districts. 
It  was  sent  to  us  first  from  Rhodesia.  Preliminary  studies  from  Rhodesian 
material  were  made,  and  it  is  intended,  if  possible,  to  carry  out  field  experi- 
ments in  connection  with  preventive  measures  during  the  coming  season." 

The  preceding  quotation  would  seem  definitely  to  decide  the 
nature  of  the  South  African  disease  but  Klerck  (19),  in  the 
February  issue  of  the  Journal,  again  put  it  in  the  doubtful  cate- 
gory by  the  following  remarks : 

"Wild-fire  and  angular  spot  of  tobacco  has  been  causing  considerable 
anxiety  amongst  tobacco  growers,  and  appears  to  be  spreading  rapidly. 
During  the  season  1920-21,  this  disease  was  only  reported  from  the  Govern- 
ment experiment  stations  at  Rustenburg  and  Piet-Retief.  from  certain 
farms  in  the  Piet-Retief  District,  and  one  in  the  Rustenburg  District. 
During  the  present  season  specimens  have  been  identified  from  three  more 
farms  within  fifty  miles  of  Rustenburg,  and  also  from  Groot  Marico  and 
Swaziland.  A  detailed  study  of  this  disease  and  the  organisms  concerned 
has  been  carried  out  by  Mr.  W.  E.  Schlitz,  of  this  Division,  and  the  South 
African  organism  compared  with  cultures  obtained  from  America,  and 
some  interesting  results  have  been  obtained.  The  South  African  organism 
is  identical  with  Bacterium  angulatum,  the  bacterium  connected  in  the  states 
with  angular  leaf  spot.  The  lesions  on  tobacco  leaves  found  in  the  field 
and  those  produced  by  inoculation  resemble  'wild-fire'  but  the  organism 
concerned  is  not  the  'wild-fire'  organism,  B.  tabacum,  which  has  not  once 
been  isolated.  A  full  account  of  these  investigations  will  be  published  at  a 
later  date." 


368         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

It  is  evident  from  the  testimony,  so  far  as  published,  that  this 
disease  in  S.  Africa  needs  even  more  critical  examination  as  to 
its  relationships  and  it  suggests  to  us  that  perhaps  wildfire  and 
angular  spot  in  the  United  States  also  should  be  more  carefully 
compared.  The  following  data,  however,  satisfies  the  writers  as  to 
the  identity  of  the  African  trouble  with  the  American  wildfire. 

In  January,  receiving  a  letter  from  Wolf,  in  which  he  stated  that 
Miss  E.  M.  Doidge,  of  Pretoria,  South  Africa,  had  written  him 
that  wildfire  had  appeared  in  that  section,  we  wrote  Miss  Doidge 
and  received  the  following  letter,  dated  March  6th : 

"In  reply  to  your  letter  of  the  30th  January,  I  may  say  that  nothing 
further  has  been  published  on  the  occurrence  of  Wildfire  in  South  Africa, 
but  that  there  appears  to  be  no  doubt  as  to  the  identity  of  the  disease  which 
was  prevalent  in  our  tobacco  fields  last  season  with  the  American  Wildfire. 
I  am  sending  under  separate  cover  some  dried  specimens  as  requested." 

An  examination  of  these  specimens  from  Rustenburg  (dated  Jan. 
2,  1922)  showed  their  similarity  in  appearance  to  our  Connecticut 
disease.  Attempts  to  inoculate  pricked  greenhouse  plants  with 
water  in  which  the  crushed  infected  tissues  had  been  soaked  for 
several  hours,  were  unusually  successful  despite  the  fact  that  the 
specimens  had  been  enclosed  in  an  envelope  containing  naphthaline 
flakes,  apparently  for  the  purpose  of  disinfecting  them. 

In  the  recent  visit  to  the  New  Haven  Station,  Dr.  Butler,  of 
Kew,  England,  stated  that  he  had  seen  a  somewhat  similar  leaf 
spot  of  tobacco  in  India  or  in  the  adjacent  islands,  but  had  made  no 
special  study  of  it,  and  was  in  doubt  as  to  its  nature. 

In  the  United  States.  The  discovery  of  wildfire  in  this  country 
seems  to  have  been  made  first  in  North  Carolina,  at  least  Wolf 
and  Foster,  (31,  p.  361.)  in  191 7,  noted  it  as  a  new  disease  found 
there  in  the  seedbeds  and  fields  and  gave  a  name  to  the  germ  which 
caused  it.  Early  the  next  year  they  (32.)  published  a  scientific 
description  of  the  germ,  Bacterium  tabacum,  and  gave  a  more 
detailed  account  of  the  trouble  which  they  listed  as  also  occurring 
in  Virginia.  In  September,  1920,  Garner  (3.)  reported  it  from 
Maryland,  Chapman  (3.)  from  Massachusetts,  and  Valleau  (3.) 
from  Kentucky;  while  in  October,  Hesler  (13.)  recorded  it  from 
Tennessee  and  Johnson  (13.)  (in  litt.,  temporary  escapes  at  Madi- 
son) from  Wisconsin.  In  1921  it  was  reported,  in  June,  by 
Westbrook  (29.)  from  Georgia,  and  in  July,  by  Orton  (20.)  from 
Pennsylvania,  and  Clayton  (4,  apparently  also  reported  in  1920,) 
from  Ohio.  Besides  the  above  states  Ludwig  (10.)  in  August, 
1921,  reported  it  questioningly  from  South  Carolina,  and  the 
writers  received  in  the  fall  a  dried  specimen  from  Vermont,  sent  by 
Lutman,  that  proved  to  be  this  disease.  In  a  letter  recently 
received  from  Burger,  he  states  that  the  disease  has  now  also  been 
identified  in  Florida.  It  seems,  therefore,  to  have  been  found  in 
thirteen  or  fourteen  states  east  of  the  Mississippi  where  tobacco  is 
most  commonly  grown. 


METHODS    OF    INTRODUCTION.  369 

Iii  Connecticut.  Wolf  and  Moss'  note  that  "presumably"  wild- 
fire occurred  in  Connecticut,  was  based  on  statements  of  Johnson, 
in  charge  of  U.  S.  Department  of  Agriculture  tobacco  experiments 
in  New  England,  who  has  since  told  the  writers  that  he  saw  the 
disease  during  the  growing  season  of  19 19  at  a  certain  farm  in 
Suffield.  As  no  previous  mention  of  this  was  made  to  Station 
authorities  here,  his  observations  were  unknown  to  them  until  after 
the  definite  identification  of  the  disease  a  year  later. 

In  the  summer  of  1918  Beinhart,  at  that  time  the  U.  S.  Govern- 
ment tobacco  agent  in  New  England,  called  to  the  senior  writer's 
attention  a  leaf  spot  trouble  of  tobacco  in  a  tent  in  which  he  had 
experiments  at  Buckland.  This  trouble  seemed  to  be  different 
from  the  ordinary  spots  seen  here,  and  both  thought  it  might  be 
either  a  fertilizer  or  bacterial  spot,  but  no  study  was  made  of  it, 
and  apparently  specimens  were  not  collected,  or  if  collected  were 
lost,  so  we  cannot  be  sure  of  its  identity.  During  the  last  of  July, 
1919,  the  senior  writer  collected  an  inconspicuous  tobacco  leaf  spot 
at  East  Windsor  Hill  that  was  not  carefully  examined  at  the  time. 
Recent  more  critical  examination  of  this  specimen  shows  it  to  be 
the  wildfire,  so  far  as  one  can  be  positive  from  the  examination  of 
dried  material. 

Late  in  June,  1920,  as  stated  before,  County  Agent  Southwick 
obtained  specimens  of  an  unusual  tobacco  trouble  at  Tariffville, 
which  later  was  found  elsewhere.  Dr.  McCormick,  at  the  Hart- 
ford laboratory,  upon  examination  of  material  from  various 
sources,  showed  these  to  be  a  bacterial  trouble,  both  by  the  presence 
of  bacteria  in  the''  diseased  tissues  and  by  the  production  of  similar 
spots  on  healthy  tobacco  leaves  from  crushed  tissue  of  the  diseased 
leaves.  Specimens  of  the  disease  were  sent  by  her  to  Dr.  Smith, 
of  the  U.  S.  Department  of  Agriculture,  and  he  definitely  pro- 
nounced it  wildfire.  This  then,  was  the  first  positive  identification 
of  the  trouble  in  the  state,  so  far  as  the  writers  are  concerned. 

Following  the  newspaper  agitation  of  the  subject  in  1921,  occa- 
sional growers  have  expressed  the  belief  that  the  disease  was  not 
necessarily  new  but  that  outbreaks  of  it  had  occurred  locally  years 
before.  This  does  not  seem  very  plausible,  since  with  all  the 
United  States  tobacco  investigators  who  have  been  in  the  state,  and 
the  local  ones,  who  have  watched  the  tobacco  troubles  rather 
closely,  it  is  unlikely  that  it  would  have  entirely  escaped  detection. 
If  not  native  this  brings  up  for  consideration  the  manner  in  which 
it  may  have  been  introduced  into  Connecticut. 


Possible  Methods  of  Introduction. 

Theoretically  there  are  a  number  of  different  ways  in  which  the 
germ  of  wildfire  may  have  been  brought  into  the  state.  We  can 
discuss  them  briefly  under  the  following  headings. 


37°  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Mats,  etc.  Some  growers  have  advanced  the  theory  that  the 
germ  was  brought  in  from  foreign  countries  on  the  matting  used  to 
bale  imported  tobacco,  especially  Sumatra.  This  matting  is  some- 
times sold  to  the  growers  and  used  on  their  beds  for  shade  in 
sunny  and  for  protection  in  freezing  weather.  One  grower  who 
used  it  on  the  ground  just  before  the  plants  came  up  had  an  idea 
that  he  got  infection  in  his  seedbed  in  this  manner.  He,  at  least, 
by  this  use  obtained  favorable  moisture  conditions  for  the  spread 
of  wildfire  possibly  already  there.  If  the  disease  is  foreign  in 
origin,  it  is  quite  reasonable  to  suppose  that  mats,  etc.,  from 
infected  districts  may  have  been  the  means  of  introducing  the 
germs  here.     However,  there  is  no  direct  evidence  to  this  effect. 

Fertilisers.  Another  of  the  out-of-state  materials  used  on 
tobacco  farms  are  the  fertilizers  and  of  these  cotton  seed  meal, 
coming  from  the  south,  both  because  of  its  source  and  its  organic 
nature,  has  come  under  suspicion  more  generally  than  the  strictly 
chemical  fertilizers.  Our  attempts  to  produce  the  disease  on 
leaves  of  individual  plants  in  the  greenhouse,  by  sprinkling  cotton 
seed  meal  from  various  sources  on  them,  failed  in  every  case.  It 
would  seem,  therefore,  that  cotton  seed  meal  was  not  a  very 
probable  means  of  its  introduction. 

Tobacco  stems,  imported  from  the  south  as  a  source  of  potash 
fertilizer,  have  also  been  under  suspicion.  Ordinarily  the  grower 
does  not  use  them  in  his  seedbeds,  though  he  may  sometimes  make 
the  seedbed  on  an  old  tobacco  field  or  very  close  to  it.  Wolf  and 
Foster  (32,  p.  457.),  who  investigated  tobacco  stems  as  one  of  the 
possible  sources  of  infection,  failed  to  get  cultures  from  them,  and 
conclude  as  follows :  "Furthermore,  in  the  preparation  of  tobacco 
stems  for  incorporation  with  fertilizer  material  they  are  subjected 
to  a  sufficient  degree  of  heat  to  insure  complete  sterilization." 
Whether  the  ordinary  tobacco  stems  as  shipped  direct  from  the 
factories  after  stripping  off  the  leaves,  and  possibly  more  or  less 
mixed  with  unfermented  tissues,  are  a  source  of  infection,  has 
never  been  proven;  Such  few  attempts  at  producing  the  disease 
from  tobacco  stems  as  we  attempted  were  negative.  It  is  con- 
ceivable, even  if  unproven,  that  they  may  be  an  occasional  agent 
of  introduction,  but  now  that  the  disease  is  already  here  they  do 
not  seem  to  be  such  a  serious  menace  as  to  prohibit  their  use  for 
general  field  purposes.  For  this  possible  occasional  danger,  and 
other  reasons,  however,  it  is  unwise  to  ever  use  tobacco  stems 
on  seedbeds. 

Seed.  We  now  come  to  the  most  probable  agent  of  wildfire 
introduction  into  the  state.  Both  Fromme  and  Wolf  are  con- 
vinced from  their  studies  that  it  is  a  seed-borne  disease,  and  that 
this  is  a  common  way  in  which  it  is  carried  over  winter,  and  so 
naturally  tobacco  seed  would  most  satisfactorily  account  for  its 
distribution  to  new  districts,  especially  from  the  south,  where  the 


METHODS    OF    INTRODUCTION.  371 

disease  was  first  noticed,  to  our  own  state  where  it  appeared  more 
recently.  For  example  Wolf  and  Moss  (33,  p.  30.)  say:  "As 
has  already  been  stated,  the  pods  are  subject  to  attack,  thus  making 
it  entirely  possible  for  the  seed  to  become  contaminated." 
Fromme  (6,  p.  29.)  makes  the  following  statements  along  similar 
lines : 

"If  seed  were  selected,  from  plants  entirely  free  from-  disease  there 
would  be  no  danger  of  infection  from  this  source.  Unfortunately,  the 
diseases  are  now  so  general  that  it  is  difficult  to  find  disease  free  fields,  and 
the  selection  of  disease  free  seed  is  therefore  possible  in  only  an  occasional 
field.  Seed  treatment  is  therefore  necessary  to  insure  against  introduction 
of  the  disease  into  the  bed  on  the  seed." 

Having  shown  that  the  disease  is  carried  by  the  seed  in  some 
cases,  the  question  of  its  introduction  here  in  this  way  may  now 
be  considered.  There  is  no  doubt  that  growers,  Government  and 
Station  investigators  have  at  different  times  grown  plants  from 
seed  produced  outside  the  state  or  even  outside  the  country.  So 
far  as  we  can  learn  the  Station  has  only  upon  two  occasions,  many 
years  ago,  used  seed  that  was  grown  elsewhere.  On  one  of  these 
occasions  Sumatra  seed  from  Florida  was  obtained  for  the  first 
shade  tobacco  grown  here.  In  recent  years  we  know  personally 
of  others  who  have  used  tobacco  seed  here  that  was  grown  in 
states  where  the  wildfire  has  since  been  found.  It  is  entirely  sup- 
posable  that  the  wildfire  may  have  been  brought  in  with  this  seed 
and  escaped  especial  notice  on  the  plants  grown  therefrom. 

Just  to  show  that  seed  grown  elsewhere  has  been  used  here,  we 
quote  from  a  bulletin  by  Shamel  (23,  pp.  6,  11.)  published  some 
years  ago  before  wildfire  was  known. 

"In  all  of  the  crops  grown  from  freshly  imported  seed,  there  appeared  a 
large  proportion  of  abnormally  early,  small  heavy  leaved  types,  commonly 
called  freaks.  *  *  *  *  These  freaks  were  particularly  noticeable  in  the 
crops  grown  from  freshly  imported  Cuban  seed.  *  *  *  If  it  is  desirable 
for  the  grower  to  test  foreign,  imported  or  new  seed  of  any  kind,  it  should 
be  done  on  a  small  scale,  etc.  *  *  *  *  A  field  was  set  out  with  plants 
grown  from  imported  seed,  which  were  attacked  by  a  fungous  root  disease, 
and  all  died  with  the  exception  of  a  few  plants." 

Seedlings.  It  is  not  a  common  thing  for  seedling  plants  to  be 
brought  into  the  state  from  elsewhere.  No  doubt  it  is  sometimes 
done  on  the  border  line  of  this  state  and  Massachusetts  in  the  Con- 
necticut valley,  but  such  cases  would  hardly  account  for  the  intro- 
duction of  wildfire  since  it  was  found  here  shortly  before  it  was 
in  Massachusetts.  Upon  one  occasion  we  know  of  experimental 
plants  used  here  that  were  grown  either  at  Washington  or  Ken- 
tucky, but  here  again  we  have  no  evidence  that  they  were  infected 
either  before  or  after  they  were  brought  in.  Altogether  this  source 
does  not  seem  quite  as  probable  a  method  of  introduction  as  by 
seed,  though  within  the  realm  of  possibility. 

Upon  the  whole  it  seems  too  late  now  to  actually  prove  the  exact 


372  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

way  by  which  the -disease  first  got  a  foothold  here,  and  certainly 
no  one  intentionally  brought  it  in.  Introduction  through  seed, 
however,  seems  to  have  been  the  most  probable  method. 

Agents  of  Dispersal. 

Almost  equally  well  do  certain  of  the  ways  already  discussed, 
concerning  the  means  of  introduction  of  the  germs  into  the  state, 
apply  to  their  dispersal  over  the  state  when  once  introduced.  State 
spread,  however,  often  involves  only  short  distances  and  there  are 
additional  factors  that  need  to  be  considered.  The  discussion  pre- 
sented here,  under  similar  headings,  avoids  repetition  of  preceding 
statements  so  far  as  possible. 

Seed.  We  have  taken  for  granted  the  conclusion  of  Fromme 
and  Wolf  that  the  disease  is  in  part  seed-borne,  and  so  have  made 
no  extensive  efforts  to  isolate  the  germ  from  seed.  While  others 
have  observed  the  wildfire  spots  on  the  seed-pods,  we  failed  to  find 
any  so  affected  in  a  careful  search  during  the  season  of  1921.  In 
1920  Mr.  Southwick  gave  us  seed-pods  that  were  supposed  to  have 
shown  wildfire  spots  on  them,  but  we  failed  to  obtain  any  diseased 
seedlings  grown  from  the  same.  We  do  not  doubt  that  seed-pods 
can  become  so  infected,  but  from  our  experience  it  seems  probable 
that  this  takes  place  only  in  certain  favorable  seasons  and  perhaps 
then  not  to  so  great  an  extent  here  as  in  the  south.  There  can  be 
no  question  that  seed  may  be  contaminated  in  other  ways  than 
through  infected  seed-pods.  For  example,  in  the  process  of  blow- 
ing or  cleaning  seed  there  is  a  chance  that  seed  free  from  the  germs 
might  become  contaminated  by  dust  ladened  with  the  germs.  One 
cannot  be  too  careful,  therefore,  in  obtaining  seed  originally  free 
from  these  bacteria  to  protect  it  from  later  exposure  to  them. 
Our  experience  leads  us  to  doubt  that  seed  has  been  the  chief 
source  of  yearly  infection  in  Connecticut.  Quite  a  number  of 
farmers  have  told  us  that  their  seed  was  gathered  a  few  years 
before  the  wildfire  was  known  here  and  that  they  had  no  trouble 
with  wildfire  in  their  seedbeds  from  the  same  seed  until  last  year 
or  the  year  before.  It  would  seem  in  some  of  these  cases,  there- 
fore, that  the  seed  was  not  the  source  of  the  infection. 

On  the  other  hand  there  have  come  to  us  one  or  two  cases  where 
it  seemed  probable  that  the  seed  was  the  source  of  infection.  For 
example,  a  grower  who  was  known  to  have  had  it  in  his  fields  in 
1920,  grew  some  of  the  Round  Tip  tobacco  in  1920,  and  used  the 
seed  next  year.  The  wildfire  appeared  in  his  seedbed  where  this 
was  grown,  and  also  in  at  least  three  other  seedbeds  of  growers 
to  whom  he  had  given  the  seed.  In  two  of  these  places  it  appeared 
earlier,  if  not  confined  to  the  seedbeds  containing  this  Round  Tip 
seed.  Some  of  this  seed  was  obtained  by  us  and  planted  in  the 
greenhouse  late  in  the  season  and  at  least  one  of  the  young  plants 


AGENTS    OF    DISPERSAL.  373 

showed  a  wildfire  spot  on  a  leaf  or  two.  It  would  seem  that  this 
seed  then  may  have  been  a  source  of  spreading  the  disease  some- 
what, though  we  failed  in  our  attempts  to  isolate  the  germ  from  it. 

Seedlings.  There  is  no  doubt  that  one  of  the  most  common 
methods  of  spreading  the  disease  has  been  by  the  seedling  plants 
set  in  the  fields.  A  great  many  growers  either  do  not,  for  one 
cause  or  another,  grow  all  the  plants  they  need,  or  in  some  cases 
depend  entirely  on  outside  sources  for  the  same.  No  doubt  for 
economical  reasons  this  is  the  best  course  to  pursue  for  certain 
small  growers.  With  the  advent  of  the  wildfire,  however,  one 
needs  to  be  especially  careful  how  he  buys  his  plants.  He  cannot 
watch  another's  seedbed  as  he  can  his  own,  and  as  wildfire  is  often 
masked  in  the  plants,  he  cannot  be  sure  of  what  he  is  getting 
unless  the  plants  come  from  a  region  where  wildfire  has  not  yet 
appeared  or  he  has  evidence  that  the  plants  were  grown  under  the 
best  possible  conditions  for  its  prevention. 

We  have  heard  of  a  number  of  cases  where  persons  knowingly 
or  unknowingly  have  purchased  plants  from  seedbeds  that  con- 
tained wildfire  infected  plants.  In  some  instances  this  has  hap- 
pened where  the  purchaser  had  seedbeds  of  his  own  in  which  wild- 
fire did  not  occur  and  thus  he  brought  it  into  his  field  from  outside 
sources.  Perhaps  the  best  illustration  of  this  was  a  case  in  Suffield, 
where  a  grower  in  1920  furnished  plants  to  a  number  of  growers 
who  had  wildfire  in  their  fields  that  year  apparently  for  the  first 
time.  Yet  the  seedbeds  of  this  man  looked  unusually  well  and 
wildfire  was  not  found  in  them  until  the  planting  season  was  over. 

Tools,  Cloth,  etc.  We  do  not  have  any  direct  evidence  of 
spread  of  the  disease  by  means  of  tools,  etc.,  used  in  a  diseased 
seedbed  or  field,  carrying  the  germs  later  to  another  free  from 
the  trouble.  We  doubt  if  this  frequently  happens,  yet  a  reason- 
able amount  of  care  should  be  used  as  regards  planters,  cultiva- 
tors, etc.,  in  seeing  that  they  are  clean  when  taken  from  one  field 
to  another.  Refuse  tobacco  should  not  be  used  on  seedbeds  under 
any  condition. 

Another  factor  that  needs  to  be  taken  into  consideration  is  the 
use  of  old  tent  cloth  as  a  seedbed  covering.  If  this  came 
from  an  infected  field  the  year  previous  it  has  been  shown  by 
Fromme  and  Wolf  that  it  may  prove  a  source  of  infection.  We 
have  no  personal  evidence  along  this  line  but  do  know  that  Florida 
authorities  are  considering  barring  the  importation  of  second-hand 
tent  cloth  from  Connecticut  into  that  state.  Wolf  and  Moss  (33, 
p.  32.)  make  the  following  definite  statement: 

"When  seeds  of  known  healthy  origin  were  used  in  certain  of  these  beds 
[free  from  the  disease],  and  the  beds  were  covered  with  new  cloths,  the 
plants  remained  free  from  wildfire.  When,  however,  other  of  the  beds  were 
nlanted  with  seed  from'  the  same  source  and  covered  with  cloths  taken  from 
heds  which  h?d  ^een  affected  with  wildfire  during  the  previous  year,  the 
disease  appeared." 


374       .  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239, 

Insects.  In  the  same  article  from  which  we  have  just  quoted, 
the  writers  (p.  30.)  state,  that  they  failed  to  find  wildfire  carried 
by  thrips  that  were  abundant  on  diseased  plants  but  that, 

"Flea-beetles,  however,  are  to  be  regarded  as  carriers  of  infection,  since 
the  wildfire  organism  has  been  isolated  from  individuals  which  had  been 
feeding  upon  diseased  plants.  Transmission  of  wildfire  by  these  insects  is 
a  fact  supported  indirectly  by  the  frequency  with  which  the  disease  appears 
around  the  holes  which  they  have  eaten  through  the  leaves." 

In  Connecticut  the  most  suspicious  insect  carriers  that  we  have 
noticed  are  also  the  tobacco  flea-beetles  and  these  chiefly  in  the 
seedbeds.  We  have  frequently  seen  them  abundant  in  certain 
seedbeds  and  absent  or  infrequent  in  others.  Some  of  these  beds 
were  abundantly  infected  with  wildfire  and  often  the  halos  centered 
around  the  small  spots  which  had  been  eaten  by  the  flea-beetles. 
In  an  effort  to  confirm  this  evidence  Dr.  McCormick,  with  Mr. 
Zappe  of  the  entomological  department,  tried  to  produce  wildfire 
with  flea-beetles.  These  were  gathered  from  infected  plants,  or 
fed  with  them  for  a  short  time,  and  then  placed  on  healthy  plants 
under  bell-jars  and  imprisoned  there  for  some  days.  In  none  of 
the  plants  experimented  with  did  any  wildfire  develop.  However 
the  experiments  were  too  limited  in  number  to  be  of  great  value. 
We  are  convinced  that  they  may  in  some  cases  become  an  important 
factor  in  the  spread  of  the  wildfire  within  the  seedbeds,  and  possi- 
bly carry  it  outside  to  adjacent  beds.  Similar  experiments  with 
lice  also  failed. 

Man.  Here,  perhaps  next  to  seed  and  seedlings,  one  finds  the 
most  common  carrier  of  the  disease.  Usually  no  care  is  taken 
when  the  beds  are  pulled  that  the  workers  do  not  carry  the  disease 
to  the  other  beds  which,  after  handling  diseased  plants,  they  mifdit 
do.  Again  growers  from  one  locality  visit  seedbeds  in  another 
and  more  or  less  miscellaneous  handling  of  the  plants  occurs. 
Growers  seem  to  be  somewhat  alert  in  this  respect  now,  as  many 
of  them  have  been  rather  cautious  as  to  indiscriminate  inspection 
of  their  beds,  while  some  few  have  posted  signs  for  visitors  to 
keep  away  from  the  beds.  Perhaps  in  the  exchange  of  plants 
from  one  locality  to  another  infected  dirt  may  be  carried  in  on 
the  shoes  or  in  the  uncleaned  baskets  used  to  transfer  the  plants. 
Care  is  needed  in  these  respects  also. 

To  illustrate  how  the  disease  may  be  carried  into  a  bed  in  an 
inconspicuous  way,  which  after  it  occurs  would  be  impossible  of 
detection  if  one  did  not  have  the  facts,  we  may  cite  the  following 
personal  experience.  In  a  seedbed  at  New  Haven,  planted  under 
conditions  where  wildfire  would  not  occur,  we  tried  to  inoculate 
some. of  the  plants  with  a  fungous  disease,  somewhat  related  to 
the  blue  mold,  that  occurs  on  certain  weeds  not  uncommon  in 
tobacco  beds.     The  infected  leaves  were  gathered  twice  in  regions 


OVERWINTERING    OF   GERMS.  375 

of  the  state  where  wildfire  did  not  occur  and  these,  under  proper 
moisture  conditions,  were  placed  on  the  tobacco  seedlings  in 
marked  spots  in  the  bed.  Both  having  failed,  they  were  gathered 
a  third  time  from  a  seedbed  where  wildfire  was  common.  This 
time  the  fungus  again  failed  to  develop  but  wildfire  appeared  on 
the  plants  within  a  few  days,  at  the  particular  spot  where  the  leaves 
were  placed.  Now  this  weed,  Lambs  Quarters  (Chaeno podium 
albidum),  is  not  infected  with  wildfire  but  by  contact  with  infected 
tobacco  plants  evidently  carried  some  of  the  germs  mechanically 
on  the  leaves  to  the  experimental  seedbed  and  infection  resulted 
from  these  under  the  favorable  moisture  conditions  provided. 

Wind  and  Rain.  While  certain  weather  conditions  have  much 
to  do  with  the  development  of  wildfire  in  the  seedbed,  once  it  gams 
entrance  there,  we  cannot  be  so  positive  about  the  wind  and  rain  as 
agents  of  its  introduction  into  the  seedbed.  It  seems  reasonable 
to  suppose  that  even  if  one  did  sterilize  his  seed,  soil,  frames,  etc., 
that  the  germs  of  adjacent  soil  might  be  spattered  in  by  rains  or 
even  more  probably  be  blown  in  with  infected  dust.  This  would 
not  mean  much  if  it  were  not  for  the  fact  that  it  is  vitally  necessary 
to  keep  the  disease  entirely  out  of  the  seedbed  if  one  wishes  to 
escape  injury  in  the  field.  We  have  more  positive  observations  on 
these  points,  however,  when  it  comes  to  spread  in  the  field,  but  we 
shall  speak  of  them  later  on. 

Overwintering  of  the  Germs. 

Seeds.  Our  discussion  of  infected  seeds  under  the  preceding 
headings  will  largely  cover  the  possibility  of  one  year  old  seed 
overwintering  the  germ  and  the  re-infection  of  seedlings  the  next 
year.  Just  how  long  the  germs  can  remain  attached  to  the  dry 
seeds  and  still  retain  their  viability  is  not  known.  So  far  no  one 
has  shown  that  the  seed  itself  is  invaded  by  the  germs  so  it  is 
presumed  that  the  overwintering  is  by  germs  accidentally  attached 
to  the  seed  coats.  It  is  very  doubtful  if  such  germs  can  retain 
-their  vitality  as  long  as  the  tobacco  seed,  which  often  germinates 
fairly  well  when  eight  to  ten  years  old.  Rapp  (Okla.  Agr.  Sta. 
Bull.  131  :  37.)  has  recently  found  with  the  bacterial  blight  of  beans 
that  two  and  three  year  old  seed  gave  blight-free  plants.  This 
is  a  case  where  the  beans  themselves  are  sometimes  invaded,  and 
so  presumably  a  longer  viability  of  the  bacteria  would  be  found 
here  than  with  the  tobacco  germ,  other  things  being  equal. 

Cloth,  Sash,  etc.  We  have  no  data  of  our  own  showing  that 
the  germ  may  be  carried  over  the  winter  on  the  boards,  sash,  or 
cloth  used  on  diseased  beds  or  fields  the  previous  year.  Yet  there 
seem  to  be  sufficient  data,  as  far  as  the  cloth  is  concerned,  furnished 
by   Wolf   and   Fromme    from   the   south.     What   difference   the 


376  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

greater  severity  of  our  winters  would  have  regarding  overwinter- 
ing we  cannot  tell,  but  if  at  all  it  would  be  unfavorable  rather 
than  favorable.  Fromme  (8,  p.  I.)  has  recently  published  the 
following  incidents  to  show  infection  from  the  use  of  old  cloth. 

"The  germs  of  blackfire  (angular  spot)  and  wildfire  may  be  carried  on 
old  canvas  and  cause  infection  in  the  plant  bed.  This  was  proved  by  experi- 
ments and  also  by  the  following  cases.  R.  H.  Mantiply  of  Amherst  County 
used  seed  that  had  been  treated  but  did  not  boil  his  canvas.  Tilden  Gooch 
used  the  same  seed  and  boiled  his  canvas.  Wildfire  and  blackfire  were  found 
in  Mr.  Mantiply's  bed  and  not  a  trace  of  either  could  be  found  in  the  bed  of 
Mr.  Gooch." 

The  only  incident  along  this  line  that  we  can  cite  for  Connecticut 
is  where  a  grower  sterilized  both  the  seed  and  the  soil  but  not  the 
sash,  cloth  or  boards  used  on  his  beds.  It  was  in  those  beds  that 
the  first  appearance  of  wildfire  in  Connecticut  in  1921  was  found. 
Apparently  in  this  case  the  germs  carried  over  in  the  materials 
used  in  making  the  seedbeds,  or,  less  probably,  were  carried  in 
from  other  unknown  sources. 

Soil.  Soil  probably  may  be  the  source  of  infection  in  some 
seedbeds  and  fields,  yet  data  absolutely  proving  this  is  difficult  to 
obtain.  We  have  little  convincing  data  along  this  line,  in  fact  so 
far  as  field  infection  goes,  it  does  not  seem  to  hold  a  very  important 
part.  But  an  occasional  holding  over  in  the  field  is  quite  a  differ- 
ent matter  from  that  in  the  seedbed  where  an  infection,  no  matter 
how  slight  or  infrequent,  can  become  an  important  means  of  fur- 
ther spread.  As  yet  we  have  made  no  attempt  to  isolate  the  germ 
from  wintered-over  soil  exposed  to  infection  the  previous  year, 
but  our  attempts  to  infect  tobacco  plants  in  the  greenhouse  directly 
with  such  soil  were  successful  in  one  out  of  several  different  trials. 
Wolf  and  Moss,  loc.  cit.  pp.  30-1,  also,  make  the  following  definite 
statement  of  a  case  in  North  Carolina : 

"In  the  tests  on  transmission  through  soil,  old  plant  beds,  which  had  borne 
diseased  plants  and  which  were  not  'fired'  prior  to  planting,  were  used.  Seed 
from  a  locality  where  wildfire  was  absent  were  sown  in  these  beds,  and  new 
cloth  was  used  as  covers.     The  disease  developed  in  some  of  these  beds." 

Tobacco  Refuse.,  It  seems  certain  that  where  a  field  or  seedbed 
has  been  badly  infected  with  wildfire  and  the  diseased  plants  were 
left  there  that  the  germs  can,  to  a  certain  extent,  be  carried  over 
in  the  more  or  less  disintegrated  tissues.  This  might  be  the  way 
it  is  carried  in  the  soil  where  it  is  supposed  to  have  survived  as 
stated  above.  Infected  tobacco  refuse  from  indoors  thrown  on 
the  fields  or  seedbeds  in  the  spring  might  also  supply  the  infecting 
germs  in  some  cases.  Our  few  attempts  to  inoculate  greenhouse 
plants  with  outdoor  overwintered  tobacco  refuse  were  successful 
in  one  case.  Evidence  along  this  line  is  also  indicated  in  the 
following  extract  from  Fromme  (8,  p.  1.)  : 

"The  disease  may  live  over  in  the  field  and  infect  the  next  crop  where 


DISTRIBUTION    IN    STATE.  377 

tobacco  follows  tobacco.  Evidence  of  this  was  obtained  in  several  cases  but 
in  some  other  cases  it  was  equally  true  that  the  disease  had  not  lived  over 
in  the  field.  It  is  believed  that  the  time  of  plowing  had  a  great  deal  to  do 
with  this  and  that  the  danger  from  this  can  be  greatly  lessened  if  the  land 
is  plowed  in  the  fall  or  early  spring,  so  that  the  suckers  have  time  to  rot  in 
the  soil  before  the  crop  is  set.  There  was  also  more  carry-over  of  the 
disease  in  the  field  during  the  mild  winter  of  1920-21  than  would  be  true  in 
ordinary  seasons." 

Detailed  Distribution  in  the  State. 

Survey.  As  previously  mentioned,  a  tobacco  disease  survey  of 
the  state  was  started  in  1920  and  continued  in  1921.  For  Hart- 
ford County,  B.  G.  Southwick,  County  Agent,  gave  valuable  help 
in  both  seasons.  In  the  spring  of  1920  Mr.  Southwick  and  Dr. 
Clinton  spent  considerable  time  on  the  seedbeds  and  during  the 
summer  Mr.  Southwick  frequently,  and  Dr.  McCormick  occasion- 
ally, made  field  trips.  The  work  was  not  undertaken  especially 
for  wildfire  investigation,  though  the  discovery  the  first  year  that 
the  disease  was  widespread  in  the  state  was  the  most  important 
feature  of  the  work,  and  largely  influenced  the  nature  of  the  work 
the  second  year.  In  1921  Mr.  Southwick,  with  Dr.  Clinton,  again 
gave  much  of  his  time  during  the  whole  season  to  the  examina- 
tion of  seedbeds  and  fields.  The  writers  are  especially  indebted 
to  him  for  first  information  about,  and  aid  in  visiting,  many  of  the 
farms  containing  infected  plants  in  Hartford  County. 

Little  work  outside  of  Hartford  County  was  done  in  1920,  but 
in  1 92 1  tobacco  seedbeds  and  fields  in  Tolland,  Middlesex,  Litch- 
field and  Fairfield  counties  were  also  examined  and  additional 
data  obtained.  County  Agents  E.  E.  Tucker,  of  Tolland,  and 
J.  H.  Fay,  of  Middlesex,  were  also  helpful  in  aiding  investigations 
in  their  respective  counties. 

/;/  IQ20.  In  the  survey  of  seedbeds  in  1920,  which  ended  about 
the  first  of  June,  no  cases  of  wildfire  were  found.  However  later 
in  the  season,  after  it  had  been  found  in  the  fields,  Mr.  South- 
wick reported  that  he  examined  one  or  two  seedbeds  from  which 
infected  fields  had  been  set,  and  found  a  few  infected  plants  in 
these.  Of  course  in  the  early  seedbed  examinations,  as  nothing 
was  known  then  about  the  presence  of  wildfire  in  the  state,  the 
disease  may  have  been  overlooked.  On  the  other  hand,  it  could 
not  have  been  at  all  conspicuous  since  care  was  taken  to  find  all 
troubles  of  any  nature  that  showed  either  on  the  leaves  or  the 
roots. 

This  same  year  in  the  fields  the  disease  was  first  discovered 
the  latter  part  of  June,  and  during  the  remainder  of  the  season 
it  was  looked  for  particularly,  and  was  eventually  found  in  twenty- 
one  other  fields.  The  known  distribution  by  the  end  of  the  1920 
season  is  shown  in  Table  I. 


378         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 


Table  I.     Known  Infections  Previous  to 

1921. 

Infected  Fields,  19 18. 

No. 

Place. 

Town. 

County. 

i(?) 

Buckland, 

Manchester, 
Infected  Fields,  1919. 

Hartford. 

No. 

Place. 

Town. 

County. 

i(?) 
1 

East  Windsor  Hill,                South  Windsor, 
West  Suffield,                         Suffield, 

Hartford. 
Hartford. 

Infected  Seed  Beds,  1920. 

No. 

Place. 

Town. 

County. 

i(?) 
1 

Floydville, 
West  Suffield, 

E.  Granby, 
Suffield, 

Infected  Fields,  1920. 

Hartford. 
Hartford. 

'No. 

Place. 

Town. 

County. 

2 
1 
1 
11 
6 

1 

East  Granby,                             E.  Granby, 
Warehouse  Point,                    E.  Windsor, 
S.  Glastonbury,                        Glastonbury, 
Suffield,                                    Suffield, 
:  Poquonock:                               Windsor, 
:Windsor     : 
Windsor  Locks,                       Windsor  Locks, 

Hartford. 
Hartford. 
Hartford. 
Hartford. 
Hartford. 

Hartford. 

In  1921.  As  this  year  especial  attention  was  given  to  the 
disease,  wildfire  was  found  in  a  great  many  more  seedbeds  and 
fields  than  in  1920.  This  was  partly  due  to  the  extra  search  for 
the  trouble,  and  also  in  part  because  it  was  undoubtedly  more  wide- 
spread and  serious  than  the  previous  year.  Of  the  122  seedbeds 
(122  growers)  that  were  examined,  it  was  found  in  fifty-one,  and 
seventy-one  were  free  from  the  trouble  so  far  as  could  be  seen  at 
the  time  of  the  examination.  As  most  of  these  beds  were  examined 
only  once  there  is  more  or  less  doubt  whether  all  of  these  listed  as 
free  remained  so  during  all  of  the  season.  In  fact  we  have  data 
showing  that,  in  a  few  cases,  beds  pronounced  apparently  free  of 
wildfire  at  the  time  of  the  examination  were  either  not  entirely  free, 
or  later  developed  the  trouble,  so  that  it  was  carried  in  sufficient 
amount  into  the  fields  to  eventually  cause  serious  injury. 

In  the  field  inspections  125  fields,  belonging  to  about  as  many 
different  growers,  were  examined  and  in  sixty-seven  wildfire  was 
more  or  less  prominent  as  compared  with  fifty-eight  fields  that 
were  apparently  free  of  the  disease.  Of  the  sixty-seven  infected 
fields  we  can  loosely  classify  them,  according  to  the  amount  of 
wildfire  that  showed  at  the  time  of  the  last  examination,  as  follows : 
thirty-four  with  little  injury,  that  is  less  than  5%  loss;  eighteen 
with  a  moderate  amount ;  eight  with  much ;  and  seven  with  very 
serious  injury,  in  a  few  cases  reaching  almost  a  total  loss.  The 
condensed  data  of  distribution  obtained  in  1921  is  given  in  Table  II. 


DISTRIBUTION    IN    STATE. 


379 


Table  II. 

Infected  and  F 

ree  Seedbeds 

AND    1 

-IELDS,    1921. 

Seed  Beds. 

Field 

s\ 

Town. 

County. 

Infected. 

Free. 

Infected. 

Free. 

Brookfield, 

Fairfield, 

0 

6 

0 

4 

Sherman, 

Fairfield, 

0 

0 

0 

9 

Barkhamsted, 

Litchfield, 

1 

0 

3 

1 

Kent, 

Litchfield, 

0 

6 

0 

0 

New  Hartford, 

Litchfield, 

0 

0 

0 

1 

New  Milford, 

Litchfield, 

0 

19 

0 

15 

Avon, 

Hartford, 

1 

0 

1 

0' 

Berlin, 

Hartford, 

0 

0 

0 

1 

Bloomfield, 

Hartford, 

3 

0 

1 

0 

Canton, 

Hartford, 

0 

0 

0 

1 

E.  Granbv, 

Hartford, 

S 

0 

7 

0 

E.  Hartford, 

Hartford, 

2 

7 

6 

2 

E.  Windsor, 

Hartford, 

1 

3 

2 

0 

Enfield, 

Hartford, 

2 

0 

5 

1 

Glastonbury, 

Hartford, 

1 

2 

0 

0 

Granby, 

Hartford, 

1 

1 

5 

0 

Hartland, 

Hartford, 

0 

0 

0 

7 

Manchester, 

Hartford, 

2 

1 

3 

0 

Simsbury, 

Hartford, 

3 

1 

4 

0 

Suffield, 

Hartford, 

3 

3 

5 

0 

S.  Windsor, 

Hartford, 

3 

1 

4 

0 

Windsor, 

Hartford, 

16 

2 

8 

1 

Windsor  Locks, 

Hartford, 

0 

0 

2 

0 

Cromwell, 

Middlesex, 

0 

9 

0 

8 

Middletown, 

Middlesex, 

0 

0 

0 

3 

Portland, 

Middlesex, 

0 

7 

0 

3 

Ellington, 

Tolland, 

4 

3 

7 

0 

Somers, 

Tolland, 

2 

0 

4 

1 

Vernon, 

Tolland, 

1 

0 

0 

0 

Totals  29. 

5 

51 

7i 

67 

58 

Distribution.  Examination  of  these  tables  shows  that  wildfire 
has  now  been  found  in  three  of  the  five  counties  of  the  state  where 
tobacco  is  grown  commercially,  namely  in  Hartford,  Tolland  and 
Litchfield  counties,  but  not,  so  far  as  we  have  data,  in  Middlesex 
or  Fairfield  counties.  By  far  the  greatest  center  of  infection  lies 
in  Hartford  county  north  of  the  city  of  Hartford.  The  disease 
has  been  found  in  over  half  of  the  towns  of  this  county  and  these 
include  nearly  all  of  the  towns  where  tobacco  is  grown  to  any 
extent.  Much  less  is  found  in  the  southern  towns  than  in  the 
northern  ones.  Hartford  county  grows  more  tobacco  than  all 
the  rest  of  the  New  England  counties  combined.  Of  the  twenty- 
nine  towns  in  the  county  four  grew  no  tobacco,  nine  in  less  amount 
than  twenty-five  acres,  while  the  other  sixteen  grew  it  as  one  of, 
if  not  their  chief  crop. 

In  Tolland  county  to  the  east  of  Hartford,  the  tobacco  region  is 
largely  limited  to  the  towns  bordering  on  Hartford  county,  and 
in  the  three  most  northern  of  these  wildfire  has  been  found  just  as 
abundantly  as  in  the  adjacent  towns  in  that  county.     Tolland  next 


380         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

to  Hartford  grows  the  most  tobacco  in  this  state,  but  not  one-tenth 
of  that  grown  in  Hartford. 

Middlesex  county  to  the  south  of  Hartford  grows  tobacco  in 
three  or  four  towns  on  its  northern  border.  Fortunately,  so  far, 
we  have  been  unable  to  find  wildfire  in  any  of  these.  As  this  dis- 
trict is  somewhat  cut  off  from  the  infected  region  to  the  north  there 
is  some  hope  that  with  care  the  disease  may  be  kept  out  of  it. 

Litchfield  county  to  the  west  of  Hartford  grows  tobacco  in  two 
distinct  regions.  One  of  these  embraces  two  or  more  of  the  towns 
bordering  on  Hartford,  and  wildfire  has  been  found  in  one  of  these 
to  a  slight  extent.  To  the  north  of  Hartford  county  come  the 
tobacco  counties  of  Massachusetts  and  wildfire  exists  there  also. 
The  counties  already  mentioned  in  general  make  up  the  tobacco 
region  of  the  Connecticut  river  valley,  the  great  tobacco  district 
of  New  England. 

The  second  tobacco  region  in  this  state  lies  in  the  valley  of  the 
Housatonic  river  in  the  northern  part  of  Fairfield  and  the  south- 
western part  of  Litchfield  county,  embraced  chiefly  in  five  or  six 
towns.  So  far  a  general  survey  of  this  region  has  not  revealed 
the  presence  of  wildfire  there.  As  this  district  is  even  more 
isolated  from  the  infected  region  than  is  the  tobacco  grown  in 
Middlesex  county,  there  is  a  still  better  possibility  of  keeping  the 
disease  out  of  it.  This  region  has  a  small  tobacco  acreage,  like 
that  in  Middlesex,  in  fact  all  of  the  tobacco  grown  in  these  three 
counties  is  less  than  that  grown  in  Tolland  county. 

Disease  in  the  Seedbeds. 

Appearance.  On  May  2,  1921,  Mr.  Southwick  asked  Dr. 
Clinton  to  examine,  at  East  Windsor  Hill,  tobacco  beds  with  which 
the  grower  was  having  trouble.  The  plants  at  this  time  were 
quite  small,  the  largest  leaves  being  about  one-half  inch  long.  The 
trouble  showed  at  the  tips,  or  less  frequently  at  the  upper  edges 
of  the  leaves,  the  infected  tissues  rapidly  rotting  and  drying  up 
(Plate  XXIX  f).  With  favorable  moisture  conditions  present  the 
rot  continued  until  nothing  of  the  blades  remained  and  the  plants 
then  shriveled  lip,  leaving  vacant  spots  in  the  beds  (Plate  XXIX  e). 
With  less  favorable  moisture  conditions  the  rotten  tissues,  of 
greater  or  less  extent,  dried  up  and  fell  off,  leaving  the  rest  of  the 
mutilated  leaf  apparently  healthy.  The  general  appearance  was 
so  much  like  the  result  of  dampening-off  fungi,  common  in  tobacco 
seedbeds,  that  we  were  surprised,  upon  a  preliminary  examination 
at  that  time,  to  find  no  suspicious  mycelium  present  in  the  tissues. 
On  the  other  hand  in  certain  intercellular  spaces  in  the  rotten  tissues 
evident  masses  of  bacteria  were  present,  so  that  we  concluded, 
temporarily,  that  the  trouble  was  of  a  bacterial  nature,  possibly 
the  bacterial  soft  rot.  Specimens  brought  to  the  laboratory  seemed 
to  confirm  this  view. 


DISEASE    IN    SEEDBEDS.  381 

About  a  week  after  the  first  examination,  Mr.  Southwick  asked 
Dr.  Clinton  to  examine  another  bed  at  Poquonock  having  similar 
trouble.  At  this  time  the  plants  had  grown  so  that  some  of  the 
leaves  were  an  inch  or  more  in  length.  While  the  dampening-off 
rot  was  present  as  before,  it  was  not  so  conspicuous,  and  there  were 
beginning  to  appear  yellow  bordering  areas  in  advance  of  these 
rotted  tissues ;  also  isolated  yellow  "halo"  spots  within  the  leaf 
blades  were  to  be  seen.  This  proved  that  the  trouble  was  the  true 
wildfire  disease.  An  examination  on  this  date.  May  8th,  also 
showed  that  the  first  beds  seen  had  now  developed  these  charac- 
teristic halo  spots. 

So  far  as  we  are  aware  this  rot  stage  of  wildfire  has  not  been 
described  before,  in  fact  Wolf  and  the  other  writers  do  not  give 
a  very  detailed  description  of  the  disease  in  the  seedbed.  We  have 
since  seen  it  in  many  other  seedbeds  and  in  every  case  the  halo  or 
yellow  spots  developed  later.  This  convinces  us  that  this  wet  rot 
is  the  first  stage  of  the  disease  in  the  seedbeds.  We  have  not 
seen  it  on  the  larger  plants.  It  seems  probable  that  with  very 
young  plants  the  first  leaves  come  in  contact  with  the  ground  and, 
if  the  wildfire  germs  are  present,  this  favors  early  invasion  through 
the  large  stomates  at  the  tip  or  margin  of  the  leaf  into  the  inter- 
cellular spaces.  This  environment,  especially  with  the  greater 
amount  of  moisture  present,  facilitates  a  rapid  rotting  of  the 
tissues  and  a  greater  production  of  bacteria.  We  have  not  as  yet 
studied  this  stage  carefully  enough  to  state  positively  that  these 
more  abundant  bacteria  are  all  wildfire  germs.  The  first  stage 
then,  according  to  our  belief,  develops  more  as  a  soft  rot  trouble 
and  chiefly  from  the  tip  or  edges  of  the  leaves  inward. 

The  second  stage  we  consider  the  halo  or  yellow  spot  which 
comes  on  quickly  after  the  first  and  on  the  somewhat  larger  plants. 
These  spots  also  may  begin  at  the  tip  or  edge  of  the  leaf,  in  which 
case  they  are  semicircular  in  outline,  or  they  may  start  more  slowly 
within  the  tissues  as  small  circular  yellow  spots  that  gradually 
enlarge,  eventually  becoming  about  half  an  inch  in  diameter. 
Their  abundance  on  the  leaf  depends  upon  the  number  of  infec- 
tions and  the  size  of  the  leaf.  In  leaves  of  plants  of  the  size  for 
transplanting  half  a  dozen  or  more  may  show  on  a  single  leaf,  and 
eventually  may  run  together  and  become  somewhat  irregular  in 
shape.  At  the  center  of  each  of  these  circular  yellow  spots  is  a 
small  whitish  or  blackish  speck,  the  point  of  origin  of  the  disease. 
In  some  cases  this  is  insect-injured  tissue,  usually  a  small  hole 
eaten  out  by  flea-beetles,  but  in  most  cases  it  is  merely  the  position 
of  the  stomates  or  breathing  pores  through  which  the  bacteria 
originally  gained  entrance  between  the  guard  cells  into  the  inter- 
cellular space  beneath.  There  they  multiplied,  killed  the  tissue 
in  their  immediate  vicinity  and  caused  a  slow  death  of  the  sur- 
rounding- tissue,  showing  first  by  the  injury  to  the  chlorophyll 
grains,  thus  forming  the  yellow  halo  spot.     Plate  XXX  a. 


382         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

The  third  stage  does  not  usually  appear  to  any  extent  in  the 
seedbeds.  This  is  where  the  yellow  spots  die,  turning  white  or 
brown,  and  if  placed  thickly  enough  on  leaves,  cause  the  interven- 
ing healthy  tissues  also  to  die.  Before  the  disease  reaches  this 
stage  the  plants  have  usually  been  transplanted  into  the  field.  Our 
experience  so  far  has  been  that  the  plants  left  in  the  infected  seed- 
bed do  not  seem  to  continue  the  disease  in  the  progressive  way 
that  one  would  expect  from  its  aggressive  first  appearance  there. 
This  may  be  because  the  moisture  conditions,  after  the  covers  are 
permanently  removed  and  watering  is  infrequent,  are  not  so  favor- 
able, but  it  is  also  probably  due  in  part  to  the  slow  growth  of  the 
thickly  set  and  competing  plants,  a  condition  that  seems  unfavor- 
able for  rapid  development  of  the  disease  anywhere. 

Conditions  favoring  the  Disease.  Of  course  the  first  essential 
is  that  the  germ  should  already  be  present  in  the  seedbed  or  be 
carried  there  in  some  manner.  We  have  already  discussed  the 
various  sources  of  infection  such  as  soil,  equipment,  fertilizers, 
and  such  active  agents  of  introduction  as  spattering  rain,  wind, 
insects  and  man.  But  even  if  present  the  active  development  of 
the  germs  depends  on  other  conditions,  such  as  the  weather,  the 
method  of  watering,  and  the  airing  of  the  beds.  These  latter 
are  quite  important  factors  and  will  be  discussed  further,  but 
before  doing  so  it  might  be  well  to  mention  one  phase  of  the  ferti- 
lizer proposition.  A  good  many  growers  have  the  idea  that  nitrate 
of  soda  has  some  influence  on  the  development  of  wildfire  in  seed- 
beds. The  only  evidence  we  have  obtained  is  that  with  the  disease 
present  in  the  seedbeds  the  liberal  use  of  this  fertilizer  incidentally 
has  some  part  in  a  more 'rapid  spread  of  the  disease,  other  things 
being;  the  same,  because  of  the  quick  growth  of  the  plants,  a 
condition  that  favors  the  spread. 

Weather.  It  was  quite  evident  in  the  spring  of  1921  that  there 
were  certain  periods  in  which  seedbed  infection  appeared  and 
progressed  more  rapidly  than  at  other  times.  The  first  favorable 
period  was  when  the  plants  were  quite  young,  about  the  first  of 
May,  as  has  already  been  pointed  out.  After  this  first  outbreak, 
due  in  part  to  the  greater  care  given  the  seedbeds  by  the  growers 
because  of  the  agitation  started  against  wildfire,  the  spread  did 
not  seem  so  rapid,  and  certainly  infected  plants  were  not  so 
conspicuous  in  the  beds. 

During  the  first  part  of  the  week  of  May  22-28  there  were 
several  days  of  cold  wet  weather  so  that  by  the  end  of  the  week 
there  began  a  second  outbreak  that  was  even  more  conspicuous 
than  the  first  because  of  the  large  size  of  the  plants  at  this  time 
and  the  consequent  prominent  halo  spots  that  appeared  abun- 
dantly on  the  leaves.  Even  when  plants  were  selected  from  beds 
that  did  not  show  the  disease  to  the  ordinary  observer,  the  grower 
did  not  always  escape  trouble  in  the  field  because  incipient  or 
masked  infections  were  already  there. 


DISEASE    IN    SEEDBEDS.  3%3 

Glass  versus  Cloth.  The  grower  cannot  control  weather  condi- 
tions, though  he  can  usually  provide  somewhat  against  their  ill 
effect.  For  example  he  can  help  by  the  type  of  covering  used  in  the 
seedbeds.  Our  inspections  in  the  infected  regions  indicated  that 
the  beds  with  glass  are  less  likely  to  develop  serious  cases  of  wild- 
fire than  the  cloth  beds.  If  we  take  the  percent,  each  of  glass  and 
cloth-covered  beds  that  developed  wildfire  as  compared  with  those 
free,  as  shown  by  our  total  inspection,  we  find  that  the  cloth  beds 
really  had  a  much  smaller  percentage.  This  means  nothing,  how- 
ever, as  most  of  the  growers  in  the  districts  free  from  wildfire, 
especially  in  the  Housatonic  valley,  happen  to  use  cloth  almost 
entirely,  while  in  the  infected  regions  of  the  Connecticut  valley, 
glass  seems  to  have  the  preference.  The  cloth  beds  do  not  keep 
out  the  rain  and  so  at  times  they  are  much  damper  than  the  glass 
beds.  Also  they  are  not  aired  so  well,  and  on  the  whole  they  are 
colder  and  shadier  and  water  does  not  evaporate  so  quickly  from 
the  leaves.  It  is  this  water  on  the  leaves,  if  it  stands  on  them 
any  great  length  of  time,  that  causes  serious  development  of  wild- 
fire. With  the  glass  bed  the  rain  does  not  get  on  the  plants  if 
care  is  used,  and  the  sash  can  be  partially  raised  even  in  rainy 
weather  so  that  the  plants  can  be  aired  and  water  kept  out  at  the 
same  time.  However,  if  the  sash  leaks  and  water  becomes  abund- 
ant in  spots,  wildfire  often  gets  a  start  there.     Plate  XXIX  a-b. 

Watering  and  Airing.  As  a  rule  watering  of  the  beds  should 
be  as  light  as  compatible  with  good  growth  and  should  be  made 
at  that  time  of  day  when  the  plants  have  opportunity  to  dry  off. 
Perhaps  the  early  morning  or  late  afternoon  is  the  best  time,  since 
there  is  less  likelihood  of  sun  scorch  at  these  times.  Beds  made 
on  wet  soils  or  well  protected  against  wind  are  difficult  to  keep 
dry  and  free  from  wildfire.  Much  of  the  water  that  stands  on 
the  leaves,  however,  is  water  of  transpiration  given  off  from  the 
leaves.  If  the  air  of  the  bed  is  saturated,  this  water  does  not 
evaporate  into  the  air,  but  accumulates  as  small  drops  all  over 
"the  leaves.  Airing  the  beds  prevents  this.  Airing  somewhat  at 
night,  when  there  is  no  danger  of  frost,  helps  to  keep  water  of 
transpiration  off  the  leaves. 

Susceptible  Varieties.  So  far  as  the  seedbed  inspection  revealed 
there  was  no  indication  whatever  that  the  varieties  commonly 
grown  in  Connecticut  had  any  degree  of  immunity.  Wildfire  was 
found  bad  on  Broadleaf,  Cuban,  Havana  and  Round  Tip.  There 
were  also  beds  of  each  of  these  that  showed  large,  moderate  and 
little  amounts  of  the  disease,  and  the  percent,  of  beds  showing 
these  different  amounts  was  not  very  different  for  any  of  the 
above  varieties.  Whether  particular  resistant  strains  of  the  above 
can  be  found  we  do  not  know,  but  it  seems  very  doubtful  unless  the 
nature  of  the  variety  is  changed ;  so  control  of  the  disease  will 
not  come  along  this  line,  at  least  for  some  time  to  come. 


384         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Damage.  While  we  have  seen  wildfire  very  prominent  in  certain 
beds,  if  it  were  confined  to  the  seedbeds  as  certain  fungous  troubles 
are,  we  would  not  consider  it  a  disease  of  sufficient  importance  to 
cause  much  anxiety  on  the  part  of  the  grower.  Of  course  in  the 
wet  rot  stage  it  does  cause  the  loss  of  some  plants,  clearing  out 
small  spots  in  the  bed.  Older  plants,  too,  are  often  injured 
enough  to  misshape  them  or  cause  them  to  be  smaller  and  less 
vigorous.  The  real  danger,  however,  comes  from  the  menace  of 
infected  plants  when  transferred  to  the  field.  Even  a  few  infected 
plants  in  the  bed  because  of  this  menace  are  very  undesirable, 
and  of  course  if  abundant  are  the  possible  source  of  complete  fail- 
ure of  the  crop.  The  approximate  amount  of  wildfire  in  the 
seedbeds  examined  in  1921  is  shown  in  the  following  table: 

Table  III.     Wildfire  in  Seedbeds  in  1921. 

Variety.  No.  No.  No.  No.  Free. 

Bad.  Moderate.  Little. 

Broadleaf,  3  2  9  19* 

Cuban,'  3  4  8  5. 

Havana,  436 

Round  Tip,  234 


*  Manj'  of  these  were  in  Portland  wildfire-free  district. 

**  These  were  mostly  in  the  Housatonic  wildfire-free  district. 

The  seedbed  then  is  the  strategic  point  for  control  of  the  disease, 
and  fortunately  this  is  where  it  can  be  controlled  with  the  least 
effort.  This  leads  up  to  a  discussion  of  the  best  methods  for 
control. 

Control  Measures.  Seed  Treatment.  Certain  precautionary 
measures  against  introduction  of  the  germs  and  care  in  ventilating 
and  watering  the  plants,  have  been  discussed.  In  the  south  the 
investigators  place  considerable  stress  on  seed  treatment.  We 
doubt  if  this  is  quite  so  important  a  factor  in  the  spread  of  the 
trouble  in  the  north.  While  we  have  evidence  of  its  being  carried 
by  the  seed,  there  seems  to  be  so  many  other  ways  by  which  infec- 
tion occurs  that  seed  treatment  alone  would  prove  of  little  value. 
Virginia  investigators  have  been  the  most  active  in  the  seed  treat- 
ment campaign  in  the  south.  In  1921  it  is  stated  by  Thomas 
(26.)  that  about  2,500  farmers  planted  treated  seed.  Fromme 
(6,  p.  30.)  first  advocated  soaking  the  seed  in  formalin  1  oz.  to  1 
pint  of  water  for  15  minutes.  Later  the  same  investigator  (8, 
p.  2.)  recommended  the  corrosive  sublimate  treatment,  using  1 
part  of  this  poison  to  1,000  parts  water  and  soaking  the  seed  also 
for  15  minutes.  Our  experience  with  both  of  these  treatments 
has  been  that  with  certain  seed  the  treatments,  especially  with  the 
formalin,  have  been  rather  severe,  killing  part  of  the  seed  so  that 
we  believe  that  10  minutes  is  long  enough  for  the  formalin. 
Where  seed  was  gathered  several  years  ago,  before  the  appearance 


DISEASE    IN    SEEDBEDS.  385 

of  wildfire,  or  where  gathered  recently  from  free  fields,  there  is 
no  particular  need  of  treating  it.  We  know  of  only  one  Connecti- 
cut grower  who  treated  (in  part)  his  seed  in  1921,  and  it  was  at 
his  place  that  we  first  found  the  wildfire. 

Soil,  etc.,  Sterilization.  Where  infection  has  occurred  in  the 
bed  the  preceding  year,  steam  sterilization  of  the  soil  should  be 
practiced  the  next,  or  else  the  beds  moved  to  new  land  not  in 
tobacco  recently.  If  we  were  to  judge  from  our  examination  of 
seedbeds  alone  we  would  find  that  sterilized  seedbeds  gave  a  far 
higher  percentage  of  wildfire  than  the  unsterilized  beds,  but  here 
again  it  was  a  question  merely  of  location,  since  very  few  of  the 
beds  in  the  Housatonic  valley,  which  is  free  from  wildfire,  are 
sterilized.  The  beds  should  receive  a  good  steam  sterilization,  say 
for  30  minutes  at  a  pressure  above  100  lbs.  It  is  well,  where  possi- 
ble, to  extend  this  sterilization  to  the  paths  immediately  around 
the  beds.  Sterilization  of  the  soil  and  seed  is  not  sufficient,  as  has 
been  shown  in  the  south,  so  that  this  should  include  the  boards, 
sash  and  cloth  used  in  the  construction  of  the  beds,  if  these  mate- 
rials have  at  all  been  exposed  to  the  germs.  This  can  best  be  done 
by  sprinkling  them  all  over  thoroughly  with  formalin  at  the  rate 
of  1  to  30  of  water,  and  piling  them  up  under  cover  to  dry  out 
slowly ;  or  the  cloth  can  be  boiled  for  an  hour. 

We  are  quite  sure  that  steam  sterilization  of  the  soil  alone  is  not 
effective  against  the  appearance  of  wildfire.  In  the  Connecticut 
river  valley  steam  sterilization  of  soil  is  a  common  practice,  yet 
wildfire  was  found  just  as  commonly  in  the  infected  districts  in 
the  steam  sterilized  beds  as  in  those  that  were  not.  This  was,  at 
least  largely,  because  the  seed,  boards,  sash  and  cloth  were  not 
sterilized  also.  We  know  of  no  place  where  all  of  these  precau- 
tions were  taken. 

Spraying.  In  1921  wildfire  appearing  in  the  seedbeds  in  so 
many  places,  it  was  necessary  to  devise  other  methods  of  control. 
There  were  apparently  just  two  things  that  could  be  done  under 
these  conditions,  namely,  spraying  the  beds  and  careful  watering 
and  ventilation  of  them.  Both  of  these  seemed  to  give  promising 
results  where  put  in  practice.  The  writers  had  had  no  experience 
in  spraying  tobacco  seedbeds  and  the  opinion  of  scientists  had  been 
that  spraying  is  not  generally  effective  against  bacterial  diseases. 
Bordeaux  mixture,  where  no  injury  results,  has  on  the  whole 
proved  the  most  satisfactory  fungicide,,  so  this  was  selected  for 
experimentation,  and  as  flea-beetles  seemed  to  be  concerned  with 
spreading  the  trouble,  lead  arsenate  was  added  as  an  insecticide. 
W  e  did  not  know,  however,  whether  injury  might  result  from  this 
spray,  but,  from  the  relationship  of  tobacco  to  the  potato,  with 
which  we  have  had  much  experience  in  spraying,  concluded  to  trv 
the  above  on  a  badly  infected  bed  at  Poquonock.  The  senior 
writer  sprayed  this  bed  on  May  8th,  and  the  grower  sprayed  it 


386         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

again  the  next  day.  This  was  the  first  time,  to  the  writers'  knowl- 
edge, Bordeaux  was  used  as  a  treatment  against  wildfire.  No 
harm  resulting  from  these  treatments,  at  the  meeting  at  Windsor 
of  tobacco  growers  called  to  discuss  wildfire,  Dr.  Clinton  advocated 
the  spraying  of  tobacco  beds  with  4-4-50  Bordeaux,  with  lead 
arsenate  added.  Many  growers  sprayed  their  beds  from  one  to 
several  times  during  the  rest  of  the  season  with  either  homemade 
or  commercial  Bordeaux  mixtures. 

As  a  result,  from  our  subsequent  experience  and  that  of  others, 
we  are  convinced  that  spraying  of  tobacco  beds  should  be  made 
one  of  the  routine  practices  of  tobacco  growing  as  long  as  there  is 
danger  from  wildfire.  We  have  seen  no  serious  injury  from  spray- 
ing with  Bordeaux  mixture,  though  in  some  cases  we  have  sprayed 
the  young  plants  fourteen  different  times  covering  an  interval  of 
as  many  weeks.  We  have  seen  a  little  injury  from  spraying,  of 
a  sun-scorch  type,  when  the  plants  were  uncovered  and  sprayed 
in  strong  sunlight.  Similar  injury  might  result  from  careless 
watering. 

We  have  evidence  that  plants  thoroughly  coated  with  the  spray 
do  not  become  infected  anything  like  unsprayed  plants  in  the  same 
beds.  Spraying  to  be  most  effective,  however,  must  start  before 
the  appearance  of  wildfire  and  be  continued  until  the  end  of  the 
transplanting  season.  WTe  would  start  with  the  young  plants  that 
have  just  taken  root  and  whose  largest  leaves  are  about  the  size 
of  a  thumb  nail,  and  spray  every  week  thereafter.  Spraying  we 
believe  is  the  only  remedy  that  prevents  spread  of  the  wildfire  in 
a  seedbed  no  matter  what  the  source  of  its  introduction.  Home- 
made Bordeaux  being  cheaper  and  apparently  somewhat  more 
effective,  we  prefer  it  to  commercial  brands  though  most  growers 
like  to  buy  a  prepared  mixture  rather  than  make  it  themselves. 
We  do  not  as  yet  advocate  commercial  lime-sulphur  and  have  had 
little  experience  with  the  dusts.  A  fifty  gallon  barrel  of  Bordeaux 
properly  applied  should  be  sufficient  to  go  over  once  a  six-foot 
bed  of  400  to  500  feet  in  length. 

One  cannot  be  too  careful  to  see  that  the  plants  he  is  to  set  out 
are  absolutely  free  from  the  trouble.  This  does  not  mean  that  if 
a  grower  finds  a  little  of  it  in  his  seedbed,  he  should  neglect  this  bed 
and  purchase  plants  elsewhere.  Unless  he  has  had  opportunity 
to  thoroughly  acquaint  himself  with  the  seedbeds  from  which  he 
purchases  plants  and  knows  that  they  are  free  from  this  disease 
(or  at  least  better  than  his  own  if  he  cannot  obtain  plants  from 
wildfire-disease-free  beds)  he  had  better  stick  to  his  own  beds  and 
make  efforts  to  eliminate  or  at  least  prevent  further  spread  of  the 
wildfire. 

If  a  grower  finds  that  the  best  thing  for  him  to  do  is  use  his 
own  plants  in  which  wildfire  has  appeared  because  of  his  neglect, 
he  should  start  at  once  to  attempt  to  eradicate  the  disease.     We 


DISEASE    IN    FIELDS.  387 

use  the  word  attempt  since  we  believe  it  will  be  difficult  to  absolutely 
eradicate  it  once  it  has  appeared,  although  it  may  be  so  masked 
as  to  seem  to  disappear  entirely.  Growers  in  1921  attempted  this 
by  killing  certain  beds  or  parts  of  beds,  (Plate  XXIX  d)  with  for- 
malin (one  to  fifteen  parts  water)  sprinkled  over  the  bad  spots. 
Care  in  airing  has  to  be  used  in  this  case  so  that  the  fumes  do  not 
extend  beyond  the  sprinkled  spot  and  injure  other  plants.  One 
sprinkling  will  not  always  entirely  kill  plants  of  some  size.  If  these 
spots  are  few  in  number  it  is  just  as  well  to  pull  up  all  the  plants 
in  these  spots  and  those  on  their  border  and  destroy  them.  Spray- 
ing, as  advocated  above,  should  then  be  begun  and  especial  care 
given  in  airing  and  watering,  and  the  beds  be  watched  for  any 
further  infection,  always  removing  any  suspicious  plants  at  once. 

Disease  in  the  Fields. 

General  Appearance.  The  first  stage  in  the  field  is  the  halo 
yellow  spot  state  (Plate  XXXI  a)  already  described  under  the  seed- 
bed infections.  On  the  larger  leaves  of  the  field  plants,  of  course, 
many  more  of  these  halo  spots  eventually  appear.  Naturally  badly 
infected  plants  are  rarely  set  out  by  the  growers.  Growth  of 
plants  is  slow  at  first  after  transplanting  and  little  spread  takes 
place  then.  If  the  weather  is  also  dry  no  spread  occurs,  and  as 
the  older  infected  leaves  wither  up  and  fall  off  there  comes  a  time 
when  the  disease  seems  to  have  largely  disappeared.  The  grower 
is  then  apt  to  conclude  that  his  plants  have  Outgrown  the  trouble. 
With  later  wet  or  muggy  weather  of  several  days  duration,  how- 
ever, the  wildfire  can  reappear  with  startling  suddenness.  As  the 
plants  gain  in  size  it  will  be  found  that  the  wildfire  is  largely  con- 
fined to  the  older  and  lower  leaves.  With  age  and  conditions 
favorable  for  spreading,  the  upper  leaves  also  become  infected, 
until  at  the  end  of  the  season  the  uppermost  small  leaves  of  the 
flowering  branches  may  even  show  the  trouble. 

Once  the  disease  gets  a  good  start  the  old  yellow  halo  spots 
gradually  give  place  to  white  or  brown  spots  of  varying  shades, 
the  chlorophyll  having  disappeared  and  the  tissues  die  (Plate 
XXXI  b).  This  is  when  the  serious  injury  from  the  disease  really 
begins.  These  spots  are  still  roundish  and  usually  show  a  more 
or  less  evident  yellow  border,  the  remnant  of  the  halo  stage.  If 
the  spots  are  now  abundant  enough  on  the  leaf  the  intervening 
tissue  may  die  and  the  whole  leaf  become  irregularly  spotted  and 
eventually  brittle  and  worthless.  The  final  injury  is  indicated  by 
the  number  of  leaves  thus  destroyed  and  the  partial  injury  to  the 
remaining  spotted  ones.  The  greatest  injury  comes  just  after  the 
disease  spreads  over  the  plants  during  the  period  of  wet  weather 
and  the  sun  suddenly  appears  again.  The  halo  spots  then  turn 
to  brown  irregular  burn-like  areas  (Plate  XXXI  c) .    This  transfor- 


388  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

mation  often  takes  place  quickly  and  so  probably  is  largely  a 
mechanical  injury  to  the  badly  infected  tissues.  One  grower 
claimed  that  most  of  the  injury  in  his  field  occurred  in  a  few  hours 
after  such  a  rainy  period  was  followed  by  bright  sunshine. 

Conditions  favoring  Spread.  Infected  Seedlings.  The  first, 
and  by  far  the  most  important,  factor  we  need  to  consider  in  field 
infections  is  the  seedlings  used  in  setting  out.  Our  experience 
last  year  indicated  that  if  the  grower  can  set  his  field  with  plants 
absolutely  free  of  wildfire  he  has  very  little  to  fear  from  this 
disease.  As  a  rule  the  greater  amount  of  infection  in  the  seedbed 
the  greater  amount  of  injury  one  may  expect  in  his  field.  This 
does  not  always  hold,  however,  and  it  does  not  necessarily  mean 
that  if  one  grower  has  it  bad  in  his  seedbed  and  his  neighbor  has 
only  a  moderate  amount,  that  the  former  will  have  the  poorer  crop. 
Often  the  field  conditions  are  factors  in  the  greater  or  less  spread 
of  the  disease.  It  is  likewise  true  that  a  moderate  number  of  the 
diseased  plants  scattered  over  the  field,  with  very  favorable  condi- 
tions for  spread,  can  by  the  end  of  the  season  injure  the  crop  as 
completely  as  would  a  large  number. 

It  is  always  best,  however,  to  play  safe  if  one  can  do  so.  For 
example,  we  know  of  a  grower  who  had  a  moderate  amount  of 
wildfire  develop  in  his  beds.  These  beds  were  later  sprayed  a 
few  times  and  the  disease  was  kept  down  so  that  it  no  longer 
appeared  conspicuous.  The  plants  as  a  whole  were  unusually  nice 
looking  and  healthy.  This  grower  would  not  use  these  plants 
but  went  to  a  district  some  distance  away  and  bought  plants  that 
were  known  to  be  free  of  this  disease.  The  plants  otherwise 
were  not  as  good  as  those  in  his  own  seedbeds.  A  neighbor  know- 
ing that  wildfire  had  occurred  in  this  man's  beds,  but  seeing  how 
well  they  looked,  bought  the  beds  for  his  own  use.  He  did  not 
use  especial  effort  to  throw  out  the  wildfire  plants  though  they  at 
that  time  were  not  prominent  as  such.  He  did  notice  after 
the  plants  were  set  out  that  there  were  some  in  the  field.  However, 
dry  weather  followed  and  the  wildfire  seemed  to  be  disappearing. 
Then,  suddenly,  there  came  on  a  more  favorable  period  and  the 
Wildfire  spread  rapidly  through  that  part  of  the  field  where  diseased 
plants  had  been  seen,  and  to  a  less  extent  where  they  were  not  so 
conspicuous.  He  became  alarmed  and  began  to  prime  his  plants 
earlier  than  he  naturally  would  have  done,  and  in  this  way  avoided 
a  part  of  the  very  serious  injury  that  would  have  resulted  had  the 
plants  not  been  primed.  The  other  man  grew  a  crop  not  injured 
at  all,  although  his  field  had  a  less  favorable  start  than  it  would 
have  had  with  his  own  plants.  A  little  wildfire  in  one  or  two 
spots  on  just  a  few  plants  finally  appeared,  but  whether  from  the 
soil  or  accidentally  carried  into  the  field  in  some  manner  we  could 
not  determine. 

It  is  not  an  uncommon  practice  for  a  grower  who  runs  short  of 


DISEASE    IN    FIELDS.  389 

plants  to  purchase  additional  ones  from  another  grower  without 
especial  attention  being  paid  to  them  except  their  general  vigorous 
appearance,  which  may  be  very  deceptive  so  far  as  the  presence 
of  wildfire  is  concerned.  Such  plants  in  setting  are  often  scattered 
more  or  less  throughout  the  fields  with  his  own  plants.  In  case 
they  happen  to  come  from  beds  containing  wildfire  while  his 
own  were  entirety  free,  their  presence  thus  scattered  through 
the  fields  may  largely  nullify  the  advantage  he  had  with  his 
own  disease-free  plants. 

If  it  is  necessary  to  buy  plants  outside,  one  should  be  sure 
that  they  are  as  free  from  this  trouble  as  his  own,  and  if  possible 
plant  them  in  blocks  by  themselves  to  prevent  any  outside  spread- 
ing if  infected,  or  to  protect  them  if  free,  from  his  own  possibly 
infected  plants.  We  know  of  growers  who  were  fairly  free  from 
wildfire  in  their  own  seedbeds  but  who  brought  the  disease  in  by 
purchased  plants  which  they  happened  to  keep  together  in  certain 
parts  of  their  fields,  and  as  a  consequence  the  disease  developed 
much  more  prominently  there  than  elsewhere. 

Method  of  Handling  Seedlings.  Another  factor  that  seems  to 
be  very  favorable  to  spreading  the  disease  before  planting  is  the 
manner  in  which  the  seed  plants  are  handled  after  pulling  from 
the  beds.  Often  the  plants  are  wet  down  all  over  and  allowed 
to  stand  for  some  time  before  planting.  Where  wet  closely  packed 
plants,  some  of  which  are  infected  with  wildfire,  are  left  in  the 
baskets  over  night  in  a  damp  atmosphere,  the  disease  will  spread 
further  according  to  our  experience.  If  the  plants  cannot  be  used 
soon  after  pulling,  it  is  just  as  well  to  keep  water  off  the  leaves, 
although  if  necessary  the  basket  may  be  kept  on  moist  ground  with 
a  good  air  circulation  above. 

Certain  of  the  crosses  experimented  with  at  the  Windsor  farm 
in  1 92 1  came  from  a  seedbed  in  which  wildfire  was  present.  This 
could  not  be  avoided  as  they  were  the  only  plants  of  the  kind  to 
be  obtained.  Another  mistake  was  made  in  pulling  the  plants  on 
a  Saturday  or  Sunday  and  keeping  them  in  a  damp  place  until 
Monday.  As  a  result  of  this  treatment  wildfire  developed  in  this 
field  even  worse  than  it  did  in  another  set  with  badly  diseased 
plants  as  a  wildfire  experiment.  At  least  two  growers  have  told 
us  of  a  somewhat  similar  experience  where  they  kept  wet  plants 
in  baskets  in  cellars  over  night.  These  wet  plants  were  set 
together  in  fields  otherwise  planted  with  freshly  pulled  seed- 
lings from  the  same  bed.  Wildfire  in  each  field  first  showed 
prominently  in  those  particular  parts  set  with  the  hold-over  plants. 

Infected  Fields.  The  next  point  to  consider  is,  will  a  field  set 
with  plants  free  from  the  disease  later  become  infected?  We 
believe  it  can  under  certain  conditions.  This  will  not  likely  happen, 
however,  in  such  isolated  regions  as  the  Housatonic  valley,  or  the 
towns  of  Cromwell,  Portland  or  Middletown  of  Middlesex  county. 


39°         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

It  may  not  even  occur  in  fields  in  a  badly  infected  region.  That 
it  does  occur  is  shown  in  the  example  cited  under  conditions 
favoring  spread.  In  any  case  it  is  not  likely  to  become  serious  if 
the  field  is  at  all  isolated  from  infected  fields.  Where  an  infected 
crop  was  grown  on  the  land  the  previous  year,  the  rotted  or  rotting 
leaves,  especially  of  the  suckers,  may  possibly  be  the  source  of  an 
infection  here  and  there.  The  encouraging  thing  about  this  is  that 
they  apparently  are  not  the  source  of  any  serious  field  infections. 

We  know  a  grower  who  had  a  little  wildfire  in  his  field  in  1919 
but  paid  no  especial  attention  to  it.  In  1920  in  the  same  field  he 
had  it  so  seriously  that  he  made  an  effort  to  keep  wildfire  out  of 
his  seedbed  in  1921,  with  the  result  that  the  plants  set  that  year 
were  fairly  if  not  entirely  free,  and  so  in  much  better  shape  than 
the  year  before.  His  crop  this  year  on  the  same  land  showed 
no  ill  effects  from  wildfire,  although  showing  some  slight  signs 
of  it.  This  would  not  have  been  the  case  if  the  germ  had  carried 
over  abundantly  in  the  soil,  as  the  season  on  the  whole  was 
favorable  for  the  development  of  the  trouble. 

Soil,  Fertilizers,  etc.  We  cannot  speak  very  definitely  about 
different  types  of  soil  as  regards  the  development  of  this  disease, 
since  we  have  seen  it  on  all  types,  sometimes  worse  on  one  and' 
sometimes  worse  on  an  entirely'  different  type.  In  general  we  are 
inclined  to  believe  that  a  soil  that  dries  out  quickly  would  not  favor 
the  spread  of  the  trouble  as  readily  as  a  wet  one.  Likewise  a 
field  on  a  hillside  would  not  be  so  bad  as  one  in  a  lower  or  less 
protected  position.  Yet  we  have  seen  fields  where  the  worst  infec- 
tions were  on  the  higher,  drier  spots.  This  was  when  the  field 
as  a  whole  was  too  wet,  however.  Perhaps  a  favorable  location 
for  the  spread  may  be  held  back  by  the  slight  infection  to  start 
with,  or  an  unfavorable  one  be  aided  by  an  original  heavy  infection 
of  the  plants.  In  such  cases  neither  will  prove  as  bad  as  where 
both  factors  are  favorable  for  the  rapid  spread. 

So  far  as  fertilizers  are  concerned  we  can  only  say  that  the  use 
of  any  fertilizer  that  favors  rapid  growth  is  more  likely  to  help 
infection,  during  a  period  of  weather  favorable  to  the  spread  of 
the  disease,  than  where  the  fertilization  is  such  that  slower  or  less 
satisfactory  growth  takes  place.  Our  field  fertilization  experi- 
ments were  not  extensive,  but  so  far  as  they  proved  anything  they 
showed  that  the  plants  with  added  fertilizer,  especially  that  with 
nitrate  of  soda,  giving  more  rapid  growth,  were  the  worst  infected. 

Speaking  along  this  line  before  tobacco  growers  at  Sufheld  in 
1921  Garner  (11. )>  of  the  U.  S.  Department  of  Agriculture,  said: 

"It  has  been  found  that,  other  things  being  equal,  an  increase  in  the 
nitrogen  supply  of  the  plant  increases  its  susceptibility  to  leaf  spot,  for 
nitrogen  promotes  a  rapid,  tender,  'watery'  type  of  development.  This 
conclusion  is  based  on  extensive  observations  in  the  field  by  means  of 
fertilizer  plot  tests  and  other  field  and  laboratory  studies.  *  *  *  *  As  a 
general  propostion  applying  nitrate  of  soda  or  other  quickly  available  form 


DISEASE    IN    FIELDS.  391 

of  nitrogen  to  young  tobacco  seedlings  should  be  avoided  as  far  as  possible 
and  if  used  at  all,  an  excess  should  be  guarded  against.  On  the  other  hand, 
a  liberal  supply  of  potash  in  suitable  form  tends  to  increase  the  resistance 
of  the  plant  against  leaf  spot  by  promoting  a  more  substantial  hardy  type 
of  growth.  Potash  alone  cannot  be  relied  upon  as  a  means  of  control  but 
at  times  it  is  of  great  value  and  is  to  be  recommended  as  a  safeguard  both 
in  the  field  and  in  the  seedbed." 

Rain  and  Wind.  These  factors  have  to  be  considered  somewhat 
together  since  they  often  act  simultaneously ;  at  least  wind  without 
rain  has  no  effect  unless  it  is  by  occasionally  carrying  the  wild- 
fire germs  into  fields  through  dust.  This  last  statement  is  based 
largely  on  supposition  rather  than  proof.  We  do  know  positively, 
however,  that  rainy  weather  of  some  duration,  with  or  without 
wind,  is  favorable  to  the  rapid  development  of  wildfire.  There 
were  only  two  periods  during  1921  that  favored  spread  of  wildfire 
in  the  fields.  The  first  of  these  came  the  week  of  June  26th  to 
July  2d,  the  latter  half  being  especially  favorable  for  the  spread. 
Growers  first  began  to  notice  this  increase  on  July  2d,  and  by  the 
4th  the  injury  was  very  pronounced.  Previous  to  this  time  the 
disease  had  spread  little  or  none  even  in  fields  that  were  set  with 
plants  badly  infected.  This  led  some  growers  to  believe  that  there 
was  nothing  to  fear  from  this  trouble. 

The  only  other  time  during  the  year  when  there  was  a  general 
spread  was  about  the  last  of  July  and  the  first  of  August  when 
there  was  a  similar  prolonged  moist  period.  This  was  when  the 
most  damage  occurred,  as  the  previous  period  had  spread  the 
disease  so  that  it  was  abundant  or  wide  spread  in  many  fields. 
However,  even  with  this  last  serious  development  there  were  some 
rather  badly  injured  fields  that  had  spots  in  which  the  plants  were 
not  hurt  to  any  great  extent. 

In  the  first  spread  the  rain  was  accompanied  by  a  high  wind 
that  in  itself  caused  much  damage  to  the  plants,  but  entirely 
independent  of  this  was  its  effect  on  the  spread  of  the  wildfire. 
This  wind  came  from  the  west,  or  more  accurately  from  the 
northwest.  That  it  had  something  to  do  with  the  spread  of  the 
wildfire  was  shown  in  fields  exposed  to  its  full  sweep.  Here  the 
wildfire  developed  at  first  most  prominently  on  that  side  of  the 
plants  exposed  to  the  wind.  This  phenomenon  had  been  noticed 
the  previous  year.  It  can  be  explained  by  the  dashing  of  the  rain 
drops  onto  the  ground  with  consequent  spattering  of  the  muddy 
water  containing  the  germs  onto  the  leaves.  These  germs  may 
have  been  washed  off  the  plants  or  may  have  been  carried  into  the 
soil  by  the  infected  dead  leaves  that  gradually  disintegrated  there. 
These  suppositions  are  borne  out  somewhat  by  our  infection 
experiments  with  muddy  water  from  infected  soil. 

In  contrast  to  this  condition  there  were  other  fields,  more  pro- 
tected from  the  wind,  that  showed  no  special  infection  of  the  plants 
on  one  side  over  the  other.     There  were  also  particularly  protected 


392  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

fields  or  spots  where  the  total  spread  was  not  nearly  so  great.  In 
some  of  these,  cases  other  factors  entered.  In  the  Station  field, 
for  instance,  where  the  plants  were  shaded  by  barns,  hedge  rows, 
etc.,  there  never  was  the  spread  that  there  was  in  the  more  open 
places.  Protection  against  the  wind  and  rain  accounted  for  this 
in  part,  but  it  was  also  due  to  the  slower,  smaller  growth  from 
shading  and  poorer  fertilizing.  We  saw  another  field,  protected 
on  two  sides  by  a  forest,  where  the  growth  and  the  wildfire  infec- 
tion were  both  much  less  than  in  the  more  open  and  exposed  part. 
In  a  dry  season  rather  unfavorable  for  wildfire  it  is  quite  possible 
that  the  reverse  of  these  results  might  occur  since  here  the  shaded 
parts  would  have  better  moisture  conditions. 

The  effect  of  a  rainy  or  a  dry  season  on  wildfire  development 
has  been  evident  in  the  southern  states  where  this  disease  first, 
appeared.  It  has  not  increased  each  year  but  its  severity  has  been 
entirely  regulated  by  the  moisture  of  the  growing  season.  For 
example,  in  most  of  the  southern  states  last  year  it  was  much  drier 
than  usual,  and  the  result  was  that  wildfire  was  inconspicuous. 
In  other  wet  years  wildfire  has  threatened  the  industry  by  its 
severity.  We  may  expect  similar  variations  in  this  state ;  in  other 
words,  if  one  were  able  to  foretell  the  weather  he  could  predict  the 
severity  of  wildfire  that  year. 

Distance  of  Spread.  We  have  no  records  of  the  spread  of  the 
disease  from  a  distance  into  an  isolated  field  by  means  of  wind  or 
even  by  insects.  In  fact  infection  by  these  agents  would  be  an 
extremely  difficult  matter  to  absolutely  prove,  but  so  far  as  our 
observations  go,  it  does  not  seem  that  either  is  a  common  method 
of  field  infections.  If  this  does  occur  the  infections  are  so  infre- 
quent as  to  prove  of  little  consequence.  On  the  other  hand  we 
have  seen  many  cases  where  we  are  sure  that  the  disease  has 
spread  from  infected  plants  in  the  field  to  those  near  by  and  even 
from  one  field  to  another  separated  only  by  a  short  distance.  In 
such  cases  the  spread  seems  to  go  most  rapidly  with  the  wind  or  the 
wind  driven  rain.     A  few  examples  will  illustrate  this. 

At  the  Station's  Windsor  farm  several  rows  of  disease-free 
seedlings  from  New  Haven  were  set  out  late.  These  had  badly 
diseased  plants  on  one  side  and  plants  with  little  disease  on  the 
other.  While  the  rain  storms  of  late  June  and  early  July  were 
largely  away  from  these  plants  toward  the  badly  infected,  they 
soon  became  infected,  at  first  largely  on  the  side  toward  the  badly 
infected  but  in  time  all  over.  In  another  place  disease-free 
tobacco  plants  were  beside  infected,  but  so  that  the  wind  came 
from  the  diseased  ones  to  them,  and  here  the  general  infection 
was  much  more  rapid.  A  more  isolated  field  entirely  out  of  the 
direction  of  the  wind  from  the  diseased  plants,  showed  only  slight 
infections  here  and  there,  but  mostly  on  the  end  towards  the 
diseased  plants.  The  wildfire,  however,  was  so  slow  here  in 
getting:  a  start  that  it  never  became  serious. 


DISEASE    IN    FIELDS.  393 

A  grower  near  Windsor  Locks  set  out  a  couple  of  rows  contain- 
ing infected  plants  on  one  side  of  his  field  in  which  there  was  no 
disease.  It  spread  slowly  to  the  next  row  or  two  but  not  further 
in,  at  least  not  before  the  middle  of  the  season  when  last  seen  by 
us.  Another  grower  near  Broadbrook  had  in  July  a  badly  infected 
field  with  the  last  one  or  two  rows  from  another  source  fairly  free. 
Just  beyond  these  and  a  narrow  grass  roadway  was  another  field 
almost  entirely  free,  the  wildfire  having  spread  only  to  a  few  plants 
in  the  first  row  or  two  next  the  diseased  field.  We  know  of 
another  field  at  East  Granby  badly  injured,  while  the  adjacent 
field  of  another  farmer  separated  by  a  rod  or  two  of  grass 
remained  practically  uninjured  during  the  whole  season,  the  most 
infections  being  next  the  badly  infected  field.  In  another  badly 
infected  field  at  Hockanum  wildfire  spread  only  slightly  to  the 
corner  of  a  field  overlapping  but  separated  by  a  grass  roadway. 

These  and  other  instances,  together  with  the  probable  fact  that 
the  germs  do  not  carry  over  to  any  great  extent  in  the  fields,  lead 
us  to  conclude  that  if  the  grower  keeps  the  trouble  out  of  his 
seedbed  he  need  not  fear  serious  injury  in  his  field. 

Varieties  Injured.  While  we  have  proved  that  the  different 
varieties  grown  in  the  seedbeds  showed  no  difference  in  suscepti- 
bility to  this  disease,  the  fact  remains  that  in  the  field  they  are  not 
all  injured  to  the  same  degree,  even  when  the  percent,  of  infected 
plants  set  out  was  the  same.  This  does  not  mean  that  in  the  field 
certain  varieties  acquire  immunity  but  rather  that  the  type  of 
growth  and  the  manner  of  handling  the  plants  seem  to  influence 
the  spread  of  the  disease  as  the  plants  grow  to  maturity.  In  gen- 
eral we  can  classify  Broadleaf  and  Havana  as  being  more  subject 
to  injury,  and  Round  Tip  and  Cuban  as  being  less. 

There  is  little  doubt  that  Broadleaf  on  the  whole  will  suffer 
more  from  this  disease  than  Havana,  though  fields  of  the  latter 
are  also  frequently  severely  injured.  The  large  drooping  Broad- 
leaf leaves  coming  in  greater  contact  with  the  ground,  seem  to 
offer  the  best  conditions  for  infection  of  any  of  the  varieties.  The 
fact  that  Havana  has  the  leaves  more  erect  and  so  not  so  frequently 
in  touch  with  the  ground,  especially  the  higher  ones,  seems  to 
help  lessen  infection  somewhat.  Where  Havana  plants  are  primed 
the  infection  is  somewhat  checked  by  removal  of  the  infected 
leaves  before  the  end  of  the  growing  season.  Some  growers  take 
advantage  of  this  and  by  early  priming  try  to  keep  partially  ahead 
of  the  spread,  or  at  least  pick  the  leaves  if  possible  before  serious 
injury  occurs.  This  is  never  done  with  Broadleaf  so  all  the 
leaves  are  exposed  throughout  the  season. 

Round  Tip  as  compared  with  Havana  suffered  less,  partly 
because  the  leaves  of  this  variety  are  always  primed.  Other  factors 
tending  to  lessen  its  infection  are  the  shorter  and  broader  leaves, 
separated  more  widely  on  the  stem  with  the  last  ones  borne  much 
higher  from  the  ground  and  the  more  vigorous  root  system  that 


394         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

keeps  the  plants  from  lopping  over  in  heavy  winds.  We  have  not 
had  opportunity  to  examine  a  sufficient  number  of  Round  Tip  fields 
to  state  that  these  advantages  always  hold.  We  got  some  rather 
badly  infected  plants  in  certain  of  our  field  experiments  where 
there  was  no  priming  made. 

Undoubtedly  the  Cuban  tobacco  grown  in  the  tents  suffered 
the  least  of  any  of  the  varieties  and  we  have  no  records  of  any 
very  serious  losses  with  this  variety.  Not  only  does  it  have  all 
of  the  advantages  mentioned  for  the  Round  Tip  (except  the 
strong  root  system)  but  it  also  has  the  further  one  of  partial  pro- 
tection of  the  tent  against  the  whipping  rain  storms  that  seem  to 
bring  the  most  infections.  Even  in  cases  where  we  know  consider- 
able infection  on  the  young  plants  was  carried  into  the  tents  the 
resulting  injury  was  not  nearly  as  serious  as  similar  infections 
produced  out  in  the  open  on  Broadleaf  and  Havana.  However, 
it  can  be  said  that  on  the  whole  the  grower  of  tent  tobacco  took 
more  precautions  to  prevent  this  trouble,  both  in  the  seedbeds  and 
the  fields,  than  did  the  growers  of  Havana  and  Broadleaf. 

Damage.  According  to  the  variety  and  the  degree  of  freedom 
from  the  disease  we  could  find  all  the  way  from  no  loss  up  to  a 
total  loss.  In  a  number  of  fields  we  estimated  the  damage  around 
60  to  70%.  When  a  field  is  injured  to  this  extent  it  is  very  doubt- 
ful if  it  pays  to  harvest  the  crop,  because  the  subsequent  cost  of 
harvesting,  curing,  etc.,  will  sometimes  be  greater  than  the  return 
from  such  a  crop. 

The  damage  caused  in  all  of  the  125  fields  inspected,  estimated 
at  the  time  of  the  last  inspection,  is  shown  by  varieties  in  the 
following  table.  Of  course  these  fields  were  inspected  at  different 
dates  and  some  only  once,  so  the  final  damage  may  have  been 
greater  than  given  here.  Apparently  no  further  injury  results 
after  the  crop  is  harvested,  as  there  is  no  evidence  that  the  wildfire 
spreads  on  the  leaves  after  hanging  in  the  barns. 

Variety.  Very  bad,         Bad,  Moderate,         Little,  Free. 


over  50%. 

25-50%. 

5-io%. 

Less  than  5%. 

Broadleaf, 

5 

5 

8 

12 

8 

Cuban, 

0 

0 

2 

9 

0 

Havana. 

2 

3 

6 

10 

50* 

Round  Tip. 

0 

0 

2 

3 

0 

*  Chiefly  in  the  wfldfire-free  Housatonic  valley. 

The  damage  by  wildfire  to  Connecticut  tobacco  is  more  serious, 
even  with  the  same  percent,  of  injury,  than  it  is  in  most  other 
states  for  the  simple  reason  that  all  the  tobacco  grown  here  is  for 
wrappers.  The  same  injury  to  a  leaf  used  as  a  wrapper  means 
much  more  than  it  does  to  a  leaf  used  for  a  binder,  filler,  or  for 
other  purposes.    The  injured  tissues  have  that  lifeless  quality  which 


DISEASE    IN    FIELDS.  395 

is  so  objectionable  because  of  brittleness  but  whether  or  not  the 
burn  is  affected  we  cannot  state.  In  the  field  the  infected  tissues 
do  not  often  fall  out  to  any  extent  but  are  more  subject  to  injury 
in  the  handling  during  curing,  fermentation,  etc.  The  color  is 
also  affected.  These  factors  would  not  be  so  objectionable  in 
tobacco  used  for  other  purposes.  If  the  spots  are  small  and  infre- 
quent perhaps  no  great  objection  would  be  raised  as  spots  of 
various  kinds  in  the  past  have  sometimes  been  sought  for  rather 
than  avoided.  Another  consideration  besides  the  use  to  which  the 
tobacco  is  put,  in  estimating  the  financial  loss,  is  the  value  of  the 
product.  Wrapper  tobacco  is  sold  for  a  higher  price  than  any 
other  tobacco,  and  in  the  tent-grown  reaches  its  highest  value  in  this 
country.  Therefore  a  50%  injury  to  a  dollar-a-pound  tobacco 
means  a  loss  of  fifty  cents  as  compared  with  a  loss  of  five  cents  on 
a  ten  cent  tobacco  similarly  injured.  In  view  of  these  facts  it  is 
much  more  essential  that  the  disease  be  controlled  here  than  it 
would  be  in  some  of  the  southern  states. 

Control  Measures.  What  are  the  control  measures  that  can  be 
taken  when  the  grower  finds  that  he  has  the  wildfire  in  his  field? 
In  the  first  place  these  must  be  confined  largely  to  the  early  stage, 
as  not  much  can  be  done  with  the  older  fields.  There  are  only 
two  measures  of  any  value  of  which  we  know  and  these  are:  1st, 
Destruction  of  infected  plants,  and  2d,  Removal  of  the  infected 
leaves.  A  third  measure  that  has  been  suggested  is  spraying  or 
dusting  the  plants  with  a  fungicide.  We  have  tried  spraying  in  a 
preliminary  way,  but  feel  that  even  if  this  may  be  helpful  in  retard- 
ing the  spread,  as  it  did  in  our  experiments,  it  is  generally  not 
a  practical  method  of  control  because  of  the  cost  and  the  unknown 
effect  of  the  spray  on  the  quality  of  the  mature  leaf.  The  other 
two  methods  may  be  discussed  further  under  their  separate 
headings. 

Destruction  of  Infected  Plants.  This  may  involve  only  a  few 
plants  or  the  plowing  up  of  the  whole  field.  Let  us  consider  the 
former  first.  After  setting  out  their  fields  in  1921  a  good  many 
growers  found  that  the  disease  was  showing  on  the  small  plants. 
Some  few  then  went  over  their  fields  and  removed  these  diseased 
plants  and  reset  with  healthy  ones.  Where  the  diseased  plants 
are  not  very  abundant  we  believe  that  this  is  a  good  practice.  The 
time  to  do  this  is  within  two  or  three  weeks  after  the  plants  are 
set  out  and  are  just  beginning  to  grow.  The  plants  pulled  up  we 
believe  should  be  placed  in  baskets  and  carried  off  the  field.  As 
the  plants  are  small  at  this  time  this  will  not  involve  much  extra 
labor.  Handling  of  the  healthy  plants  should  be  avoided,  and  the 
field  reset  as  soon  as  possible  with  healthy  plants.  We  doubt  if 
this  method  is  practical  after  the  plants  have  grown  to  any  con- 
siderable extent,  because  of  the  greater  amount  of  work  involved, 
and  the  resulting  unevenness  of  the  field  if  reset. 

We  have  no  positive  data  as  to  the  value  of  this  treatment  but 


396         CONNECTICUT   EXPERIMENT    STATION    BULLETIN    239. 

only  the  knowledge  that  theoretically  we  have  removed  so  many 
plants  that  would  have  served  as  centers  of  spread  under  favorable 
conditions.  Not  all  of  the  infected  plants  will  have  been  removed, 
even  with  a  second  careful  inspection  of  the  field,  as  the  disease 
will  be  so  masked  on  some  of  the  leaves  as  to  escape  detection. 
If,  however,  a  large  percentage  has  been  removed,  this  should 
help  delay  the  spread  and  under  some  conditions  certainly  would 
serve  to  protect  the  field  against  the  more  serious  injury  that  would 
have  resulted  with  a  greater  infection  to  start  with. 

Where  there  was  considerable  infection  in  a  field  some  of  the 
growers  plowed  up  the  whole  field  and  reset  with  other  plants. 
This  is  a  practice  that  can  be  followed  only  when  the  plants  are 
small  and  one  is  sure  that  the  new  plants  put  out  are  freer  of  the 
disease  than  those  plowed  up.  The  question  arises  whether  or  not 
these  plants  plowed  in  may  not  serve  as  source  of  infection  for 
the  new  plants.  We  believe  that  this  infection  is  at  least  possible 
under  some  conditions,  but  whether  or  not  it  is  ever  a  serious  men- 
ace we  have  no  data  as  yet  to  make  a  positive  statement.  We  do 
know  of  at  least  one  field  where  the  infected  plants  were  plowed 
under,  which  after  replanting  remained  fairly  free  from  the  disease 
until  danger  of  serious  infection,  at  least,  was  past.  We  heard 
of  another  field  seriously  injured  in  1920  that  was  plowed  up  when 
the  plants  were  of  some  size  and  reset,  and  in  this  case  also  the 
disease  did  not  make  any  headway  later.  The  late  replanting  gave 
a  fair  growth  but  quality  was  lacking  in  the  crop.  This  is  a  thing 
that  must  be  taken  into  consideration  in  plowing  up  infected  fields, 
namely,  it  must  be  done  in  time  so  that  the  replanted  crop  can 
thoroughly  mature.  The  season  of  192 1  was  more  favorable  than 
most  seasons  in  this  respect  since  the  frosts  held  off  unusually  late, 
allowing  late  planted  fields  to  mature. 

It  is  not  always  easy  to  decide  whether  or  not  to  plow  up  a 
field.  We  know,  for  example,  of  a  grower  of  tent  tobacco  who 
had  a  considerable  amount  of  wildfire  in  the  plants  when  set  out. 
The  plants  were  of  some  size  when,  because  of  the  abundance  of 
wildfire,  he  was  advised  to  plow  up  the  field.  Because  of  the  diffi- 
culty of  plowing  them  under,  he  let  them  grow  finally,  and  got  a 
crop  fairly  free  from  injury.  He  might  not  have  been  so  lucky  if 
this  crop  had  been  Broadleaf,  for  no  doubt  the  tent  and  priming 
helped  to  keep  down  the  disease  in  this  case.  Each  grower  will 
have  to  settle  his  own  policy  after  careful  inspection  of  his  field  as 
no  hard  and  fast  rule  can  be  laid  down  to  govern  all  cases. 

Removal  of  Infected  Leaves.  If  the  infected  crop  has  begun 
to  grow  and  it  is  too  late  or  inadvisable  to  plow  it  up,  there  is 
still  a  possibility  of  partial  control  by  picking  off  all  lower 
leaves  showing  any  signs  of  infection.  In  fact,  if  the  plants  have 
only  a  few  infected  leaves  it  is  better  to  pick  off  all  the  leaves 
below  these  as  well,  whether  or  not  they  show  halo  spots.  On 
such  leaves  the  infection  may  be  present  and  still  not  be  very 


DISEASE    IN    FIELDS.  397 

evident  because  of  their  yellowed  and  often  withered  condition. 
They  are  of  no  commercial  value  anyway.  On  young  plants  the 
removal  of  these  leaves,  if  there  are  still  several  healthy  green  ones 
remaining,  does  little  injury  to  the  growth.  After  the  plants  have 
made  some  growth  it  may  be  found  that  the  first  removal  was  not 
sufficient  and  a  second  or  even  a  third  be  required.  In  the  latter 
case  if  many  large  leaves  are  removed  the  plants  are  later  hindered 
in  their  growth.  In  other  words,  the  removal  of  leaves  once  or 
twice  before  or  shortly  after  the  plants  have  started  to  grow  seems 
practical,  but  if  required  again,  where  the  final  leaves  of  com- 
mercial value  have  to  be  removed,  it  is  of  very  doubtful  value. 
The  removal  therefore  should  be  with  fairly  small  plants  and 
include  leaves  of  no  commercial  value  and  should  take  place  before 
there  has  been  much  chance  for  field  infection  from  the  infections 
actually  brought  from  the  seedbed.  Leaves  removed  should,  for 
greater  security,  be  carried  off  the  field. 

We  know  of  one  or  two  growers  who  practiced  this  removal 
and  felt  that  it  had  resulted  in  a  more  limited  field  infection. 
These  were  cases  of  Cuban  tent-grown  tobacco  and  it  looks  as  if 
the  best  results  would  be  obtained  with  this  variety.  These  lower 
leaves  are  of  no  value  and  often  are  picked  off  and  thrown  on  the 
ground  so  that  only  a  little  more  care  and  effort  is  required  to 
do  a  good  job.  The  advantage  would  be  to  get  rid  of  a  consider- 
able number  of  infections  and  also  to  remove  those  lower  leaves 
that  come  in  contact  with  the  ground  from  which  secondary  infec- 
tion might  start.  The  usual  priming  that  follows  in  these  fields 
then  should  help  to  keep  in  check  further  serious  injury. 

With  primed  Havana  similar  treatment  might  be  helpful  to  a 
less  degree  but  with  unprimed  Havana  and  Broadleaf  the  value  is 
uncertain.  In  these  cases  it  would  naturally  be  limited  to  the 
very  early  stages  of  growth.  Once  it  becomes  necessary  to  pull 
off  the  large  or  commercial  leaves,  it  is  doubtful  if  one  can  check 
the  disease  enough  to  pay  for  the  extra  expense  of  removal,  loss 
of  leaves  removed  and  injury  to  the  growth  of  the  plant  that 
results.  We  know  of  a  few  cases  of  infected  Broadleaf  of  some 
size  where  removal  under  these  conditions  did  not  seem  to  be  of 
any  value. 

Our  own  experiments  at  Windsor  were  rather  unfavorable  to 
removal  of  leaves  as  a  means  of  retarding  the  spread  of  the 
disease.  The  leaves  here  were  removed  from  some  of  the  rows 
once  and  from  others  twice,  with  check  rows  with  leaves  unre- 
moved.  Eventually  the  disease  spread  about  as  badly  to  those 
rows  with  leaves  removed  once  or  twice  as  to  those  with  leaves 
unremoved,  and  the  second  late  removal  checked  somewhat  the 
rapidly  growing  plants.  In  this  experiment,  however,  there  was 
no  protection  against  re-infection  of  the  plants  after  their  infected 
leaves  were  removed,  since  they  were  always  side  by '  side  or 
nearly  so  with  rows  from  which  no  leaves  were  removed.     Because 


398  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

of  this  it  is  quite  possible  that  much  of  the  value  of  removal  was 
lost  compared  with  an  entire  field  in  which  total  removal  is 
practiced. 

Seedbed  and  Field  Experiments. 

These  are  miscellaneous  experiments  tried  during  1921  in  an 
effort  to  learn  something  about  the  development,  spread  and  con- 
trol of  wildfire.  It  is  partly  from  these  and  the  laboratory 
studies  that  our  preceding  statements  have  been  made.  Quite  a 
number  of  the  field  experiments  were  not  followed  closely  after  it 
became  evident  that  wildfire  was  general  in  the  plants  experimented 
with,  as  little  further  information  was  to  be  gained.  Upon  the 
whole  we  did  not  aim  to  collect  figures  to  illustrate  the  results, 
but  rather  depended  on  general  examinations. 

Spraying  and  Dusting  Seedbeds.  It  must  be  borne  in  mind  that 
the  treatment  of  seedbeds  was  begun  in  most  cases  after  the  wild- 
fire appeared  in  them.  In  a  few  cases  wildfire  did  not  develop 
much  further,  or  at  all,  either  in  the  sprayed  or  unsprayed  parts, 
so  here  conclusions  could  be  drawn  only  of  the  general  effect  of 
the  fungicides  on  the  young  plants.  In  most  cases  Bordeaux 
mixture  was  used,  and  this  was  usually  the  homemade  4-4-50 
strength,  and  almost  always  had  lead  arsenate  in  it.  In  one  or 
two  cases  Bowker's  Pyrox  or  other  commercial  Bordeaux  mix- 
tures were  used,  and  in  one  place  Bordeaux  dust  was  compared 
with  Bordeaux  mixture.  Altogether  spraying  tests  were  made  in 
nine  different  beds  in  the  following  places :  three  at  Rainbow ; 
one  at  Poquonock ;  three  at  East  Hartford ;  one  at  East  Windsor 
Hill ;   one  at  New  Haven. 

Seedbeds  1-2,  Rainbow.  Each  seedbed  had  the  same  treatment 
and  other  conditions  were  the  same :  Havana,  glass,  soil  steri- 
lized, flea-beetles  rather  abundant;  used  lead  arsenate  in  each 
spraying ;  sprayed  five  times,  May  9,  May  20,  May  27,  June  3,  June 
20 ;  wildfire  scattered  irregularly  in  spots  in  beds  before  treatments 
began.  Plot  1,  Check,  no  treatment  (except  received  spraying  first 
time),  35  feet  of  each  bed.  Plot  2,  Homemade  Bordeaux,  4-4-50, 
on  twenty-five  feet  of  each  bed.  Results:  Final  examinations 
showed  that  wildfire  did  not  develop  further  in  the  sprayed  plots, 
and  while  its  spread  in  the  checks  was  not  so  rapid  as  earlier,  the 
difference  between  them  was  marked  by  the  characteristic  halo  spots 
on  unsprayed  plants  close  up  to  the  line  separating  the  two  plots. 
Likewise  the  flea-beetle  injury  was  much  more  evident  on  the 
unsprayed  plants.  The  grower  did  not  use  these  beds  (he  also 
destroyed  with  formalin  four  other  more  badly  infected  beds,  see 
Plate  XXIX  d)  but  bought  disease-free  plants  elsewhere ;  he  had  no 
trouble  in  his  fields.  Another  farmer  bought  the  experimental 
beds  but  we  did  not  examine  his  field  except  very  early  in  the  season 
when  very  little  wildfire  showed. 

Seedbed  3,  Rainbow.     Same  place  and  variety  as  beds  1-2,  but 


SEEDBED    EXPERIMENTS.  399 

with  soil  unsterilized,  cloth  covers  and  planted  very  late,  after 
appearance  of  wildfire  in  the  other  beds.  Spraying  was  started 
on  the  very  young  plants  soon  after  coming  up  (largest  leaves  size 
of  finger-nail)  and  before  any  wildfire  showed.  Care  was  used 
in  watering,  and  airing  was  always  good.  Sprays,  all  containing 
lead  arsenate,  applied  seven  times,  as  follows :  May  27,  June  3, 
June  10,  June  20,  June  28,  July  6,  July  14.  Plot  1,  Check,  no 
treatment,  first  20  feet  of  bed.  Plot  2,  General  Chemical  Co. 
Bordeaux,  t,j/2  lbs.  to  50  gals,  water,  next  20  feet  of  bed.  Plot  3, 
Bordeaux  mixture,  homemade,  4-4-50,  20  feet  of  bed.  Plot  4, 
Bowker's  Pyrox,  10  lbs.  to  50  gals,  water,  last  20  feet  of  bed. 
Results:  June  20th  wildfire  appeared  in  the  Check  plot  in  a  single 
spot,  and  eventually  showed  abundantly  in  several  spots,  one  or 
two  entirely  isolated  from  first.  Weather  was  not  very  favorable, 
except  once  for  spread,  so  disease  finally  became  more  or  less 
masked.  Eventually  it  also  appeared  in  a  very  small  spot  in  Plot 
2,  but  did  not  seem  to  spread.  This  plot  was  nearest  to  the  check, 
and  seemed  least  protected  by  spray  as  the  sediment  was  not  so 
evident  on  leaves  after  spraying.  No  wildfire  was  seen  at  any 
time  in  the  other  two  sprayed  plots. 

Seedbed  4,  Poquonock.  Havana,  soil  sterilized,  beds  with  glass 
but  uncovered  most  if  not  all  of  the  time.  Wildfire  showed  a  little 
in  spots  over  bed  before  treatment  began.  Spray,  containing  lead 
arsenate,  was  applied  five  times.  May  11,  May  15,  May,  20,  May  27, 
June  3.  Plot  1,  Check,  no  treatment  (except  received  spray  the  first 
time)  first  12  feet  in  bed.  Plot  2,  Bordeaux  mixture,  homemade. 
4-4-50,  on  rest  of  bed,  50  feet.  Results:  This  and  the  other  beds  of 
the  grower  were  among  the  first  to  show  wildfire,  but  because  of 
care  in  airing  and  one  or  two  general  sprayings,  the  disease  never 
'became  very  prominent  after  its  first  appearance.  In  our  experi- 
mental plots  there  was  no  further  development  in  the  sprayed  one. 
and  apparently  but  little  more  in  the  check.  However,  plants  used 
from  the  other  beds  developed  a  conspicuous  wildfire  outbreak  in 
the  field  in  early  July. 

Seedbed  5,  East  Hartford.  Broadleaf,  soil  sterilized,  glass  alter- 
nating with  cloth  sash.  Wildfire  appeared  shortly  before  first 
spraying,  spotting  bed  more  in  some  plots  than  in  others.  Used 
lead  arsenate  in  all  sprays  which  were  applied  four  times,  May  18, 
May  24.  June  1,  June  8.  Plot  1.  Check,  no  treatment,  8  feet  at 
end  of  bed.  Plot  2,  Bordeaux  mixture,  homemade,  4-4-50,  next 
40  feet.  Plot  3,  Bordeaux  mixture,  homemade,  2-2-50,  32  feet  of 
bed.  Plot  4,  Bowker's  Pyrox,  10  lbs.  to  50  gals,  water,  last  48 
feet  of  bed.  Results:  Before  treatment  most  wildfire  showed  in 
the  Bordeaux  plots,  but  did  not  increase  afterward  and  really 
became  less  conspicuous ;  also  no  further  development  occurred  in 
the  Pyrox  plot.  The  check  plot  had  least  of  any  to  start  with 
and  because  of  good  airing  and  watering,  it  did  not  increase  verv 


400         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

much.  Care  was  used  in  selecting  plants  from  this  and  bed  6  for 
field  planting,  and  wildfire  was  never  conspicuous  there. 

Seedbed  6,  East  Hartford.  Same  grower  and  conditions  as  bed 
5,  but  only  three  sprayings  given,  the  first  being  .omitted.  Experi- 
mental plots  1-4  with  same  treatment  as  in  bed  5.  Wildfire  more 
prominent  in  this  bed  when  treatments  began,  especially  in  the 
sprayed  plots.  Results:  Wildfire  checked  in  all  the  sprayed  plots, 
as  there  was  no  further  development  there,  but  in  the  check  plot 
it  developed  further  in  spots.  A  little  burn,  of  the  sun-scorch 
type,  resulted  after  the  second  spraying  of  June  1st,  probably 
because  made  in  too  strong  sunlight  on  recently  uncovered  plants. 

Seedbed  7,  East  Hartford.  Same  grower  as  of  beds  5-6  but 
bed  late  planted  and  in  more  shaded,  damper  spot,  covered  with 
cloth  only.  Four  treatments  on  same  dates  as  bed  5.  Plot  1, 
Check.  Plot  2,  2-2-50  Bordeaux.  Plot  3,  4-4-50  Bordeaux. 
Results:  Very  good  place  for  development  of  wildfire  but  germs 
apparently  absent  as  no  wildfire  was  seen  either  before  or  after 
the  experiment  in  any  of  the  plots.     No  spray  injury. 

Seedbed  8,  East  Windsor  Hill.  Broadleaf,  beds  not  sterilized, 
glass.  No  lead  arsenate  used  in  any  of  the  three  sprayings  (as 
flea-beetles  not  evident)  made  on  May  18,  May  24,  and  June  1. 
Wildfire  evident  in  about  two-thirds  of  bed  before  spraying  began. 
Plot  1,  Check,  no  treatment,  8  feet  of  bed.  Plot  2,  Bordeaux, 
homemade,  4-4-50,  remaining  40  feet.  Results'-  Wildfire  was 
checked  entirely  in  sprayed  part  of  bed  and  became  less  conspicuous 
in  time.  In  the  check  it  developed  so  that  it  was  more  prominent 
even  though  masked  and  hidden  by  the  crowded  plants  at  the 
end  of  the  experiment.  Other  beds  were  sprayed  at  least  once  by 
the  grower,  kept  well  aired,  and  he  took  his  plants  only  from  the 
least  infected  parts  of  the  beds.  However  he  got  a  fair  sprink- 
ling of  infected  plants  in  the  field,  and  eventually  suffered  about 
15%  loss  from  wildfire.  If  he  had  not  used  this  care  in  the  beds 
and  in  selecting  his  plants,  his  loss,  without  doubt,  would  have  been 
much  greater. 

Seedbed  9,  New  Haven.  Havana,  soil  unsterilized,  cloth  cover. 
This  was  planned  to  test  value  of  dusting  as  compared  with  spray- 
ing, using  both  Bordeaux  and  Lime  Sulphur  dust  as  well  as 
Bordeaux  mixture  and  commercial  L.  &  S.  solution.  Some  of  the 
plots  whose  seed  was  soaked  with  water  containing  wildfire  germs 
did  not  come  up  so  only  Bordeaux  mixture  and  Bordeaux  dust 
were  used.  The  experiment  was  started  in  the  fall  and  five  treat- 
ments were  given  in  the  seedbed,  on  Oct.  4,  Oct.  10,  Oct.  19,  Oct. 
26,  and  Nov.  6.  After  the  last  treatment,  however,  a  few  plants 
from  each  plot  were  transferred  to  small  flats  in  the  greenhouse 
and  treatments  continued  there  during  the  next  nine  weeks.  Plot 
1,  Check,  no  treatment,  seed  sterilized  with  formalin.  Plot  2. 
seed  and  soil  sprayed  with  wildfire  germs  before  planting ;  dusted 
well  each  time  with  Glidden's  Bordeaux  dust.     Plot  3,  seed  and 


FIELD    EXPERIMENTS.  4QI 

soil  sprayed  with  wildfire  germs  before  planting;  sprayed  well 
each  time  with  homemade,  4-4-50  Bordeaux.  Results:  No  wild- 
fire developed  on  any  of  the  plants  in  the  seedbeds  or  in  the  green- 
house. No  evident  injury  resulted  from  spraying  with  Bordeaux 
mixture  fourteen  times.  Soon  after  dusting  began  it  was  seen 
that  these  plants  were  yellowing  and  injured  somewhat ;  they  were 
more  or  less  stunted  by  subsequent  treatments  and  never  grew  as 
large  as  those  sprayed. 

Killing  Plants  with  Formalin.  This  was  tried  only  in  two  beds. 
Formalin  at  rate  of  1  to  15  of  water  was  liberally  sprinkled  with 
an  ordinary  sprinkling  can  on  marked  wildfire  spots.  The  next 
day  the' plants  were  all  dead;  The  photograph  (Plate  XXIX  c) 
shown  here  was  taken  several  days  later.  Care  was  used  not  to  get 
the  liquid  outside  the  spots  and  the  beds  had  the  sash  off  at  the  time. 
No  injury  showed  outside  the  sprayed  spots.  We  have  seen  older 
beds  where  all  the  plants  were  sprayed  and  many  leaves  killed  but 
the  plants  started  to  grow  again.  It  is  evidently  harder  to  kill 
large  than  small  plants,  but  in  these  cases  less  liquid  or  a  weaker 
strength  may  have  been  used.     See  Plate  XXIX  d. 

Field  Experiments  with  Infected  Seedlings.  These  were  experi- 
ments with  plants  of  different  varieties  selected  from  various 
infected  beds  and  transplanted  at  New  Haven  and  the  Windsor 
tobacco  farm,  where  they  could  be  especially  watched  to  see  how 
the  disease  progressed  later. 

Windsor  Experiments.  The  tobacco  plants  were  set  out  June 
7th  at  the  Windsor  tobacco  farm  with  eight  rows  to  a  plot,  except 
plot  5  which  had  six.  The  rows  averaged  about  150  plants.  The 
Broadleaf,  Havana  and  Round  Tip  plants  in  plots  1,  3  and  5  were 
obtained  from  seedbeds  bad  with  wildfire,  at  least  in  spots,  and 
infected  seedlings  were  selected  as  far  as  possible.  As  check  to 
these,  plots  2,  4  and  6  were  set  with  plants  free,  or  nearly  free 
from  wildfire.  Table  IV  shows  the  results  of  the  examination 
of  all  the  plants  on  June  28,  before  there  was  any  appreciable 
spread  of  wildfire,  but  late  enough  for  any  masked  seedbed  infec- 
tions to  show.  The  check  plots  had  only  a  few  slightly  infected 
leaves  and  these  were  all  removed  on  this  date,  check  plot  6  being 
the  worst  of  these  but  still  with  less  than  3%  slightly  infected 
plants  as  compared  with  67%  in  the  Havana  wildfire  plots.  There 
was  no  check,  wildfire-free,  Broadleaf  plot.  After  the  July  4th 
spread  the  disease  became  general  in  the  infected  plots  and  even 
spread  considerably  into  the  check  or  free  plots.  In  these  it 
appeared  most  abundantly  in  the  rows  next  the  infected  plots  and 
by  the  end  of  the  season  had  spread  generally  through  the  rows, 
but  never  so  bad  as  in  the  wildfire  plots.  The  west  end  of  all  the 
plots,  both  wildfire  and  check,  never  developed  nearly  as  much 
wildfire  as  the  east  end  which  was  more  exposed  and  better 
fertilized. 


402  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Table  IV.     Wildfire  Plants  on  Station  Field,  Windsor. 


Seedlings 

Total 

Inf. 

% 

Plot.  Row. 

Locality. 

Variety. 

Condition. 

Plants. 

Plants. 

Infected 

1         1-8, 

Rainbow, 

Broadleaf, 

Bad, 

1113 

439 

39-0 

2        9-16, 

Suffield, 

Havana, 

Free, 

1375 

1 

.08 

3       17-24, 

Suffield, 

Havana, 

Very  Bad, 

1254 

837 

67.0 

4       25-32, 

Windsor, 

Round  Tip, 

Trace, 

1 197 

13 

1.0 

5       33-38, 

Suffield, 

Round  Tip, 

Bad, 

777 

386 

50.0 

6      39-46,       Windsor,     Round  Tip,    Trace,  1006  32  3.0 

While  the  examination  of  June  28  showed  that  the  Havana  wild- 
fire Plot  3  had  the  highest  infection,  67%,  Round  Tip  Plot  5  next 
with  50%,  and  Broadleaf,  Plot  1,  the  least  with  39%,  after  the 
favorable  weather  ending  July  4th  it  was  seen  that  the  spread  was 
greatest  in  the  Broadleaf,  next  in  the  Havana,  and  least  in  the 
Round  Tip.  This  agrees  with  our  experience  elsewhere  that  these 
varieties  are  injured  differently  in  the  field.  While  no  counts  were 
made  over  the  whole  plots  as  on  June  28th,  counts  on  July  27  of 
a  few  of  the  unsprayed  plants,  given  in  Table  VIII,  at  the  least 
injured  end  of  the  field  bring  out  this  same  variation  in  spread 
according  to  variety.  For  example,  all  8  unsprayed  Broadleaf 
plants  taken  as  they  came  in  the  row  were  infected  and  had 
55  infected  leaves  showing  1576  wildfire  spots,  as  against  19 
infected  Ffavana  plants  similarly  counted  with  only  71  infected 
leaves  containing  602  spots  and  16  out  of  19  counted  Round 
Tip  plants  with  48  infected  leaves  containing  204  spots.  Figur- 
ing from  this  data  the  ratio  of  spots  per  plant  in  each  variety, 
the  difference  would  be  still  more  marked  since  the  Broadleaf 
plant  would  have  196  spots,  the  Havana  32,  and  the  Round  Tip 
only  11,  despite  the  fact  that  the  Havana  seedlings  were  the  worst 
and  the  Broadleaf  the  least  infected  to  start  with. 

New  Haven  Experiments.  At  New  Haven  the  plants  from 
different  sources  were  set  out  in  small  numbers  in  a  garden  plot 
so  that  they  were  all  close  together.  There  was  no  very  evident 
development  until  July  5th,  just  at  the  end  of  the  favorable  moist 
weather  for  spreading  already  mentioned.  Before  this  time  in 
most  cases  the  disease  became  less  rather  than  more  evident,  as  the 
infected  leaves  matured  and  disappeared.  In  one  case  (No.  1585) 
however,  the  disease  became  more  evident  soon  after  planting  as 
it  was  masked  in  the  seedlings  when  set  out.  The  disease-free 
plants  from  New  Milford  remained  practically  free  until  July  5th, 
when  they  became  more  or  less  abundantly  infected,  largely  from 
infected  leaves  previously  buried  under  them,  but  partly  by  spread 
from  the  nearby  infected  plants.  We  shall  speak  of  these  later. 
The  condition  of  all  plants  as  regards  wildfire  on  July  11,  together 
with  other  data,  is  shown  in  Table  V.  An  examination  of  these 
data  shows  that  no  varieties  had  any  pronounced  freedom  from 
the  disease  when  closely  planted  in  small  plots  with  others,  with  no 
topping,  priming,  etc.,  to  limit  the  spread;  in  other  words  the 
Cuban  tobacco  became  infected  almost  as  badly  as  the  Broadleaf. 


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404         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Infection  from  the  Soil.  Certain  of  the  wildfire- free  Havana 
plants  (1588,  Table  V.)  from  New  Milford  had  wildfire  leaves 
buried  in  the  soil  under  them  on  June  15th.  After  the  first  field 
outbreak,  showing  July  4th,  these  plants  became  abundantly 
infected.  As  they  were  near  other  wildfire  plants  the  infection 
may  have  in  part  come  from  these,  but  we  believe  most  of  it  came 
from  the  germs  in  the  soil  from  the  buried  leaves,  as  the  eight 
check  plants  (1588a)  under  which  no  leaves  were  buried,  had 
only  13%  with  moderate  and  bad  infections  as  compared  with 
63%  in  the  others.  These  checks,  too,  were  more  exposed  to 
the  other  infected  plants  nearby.  The  infections  also  showed 
more  on  the  sides  of  the  plants  under  which  the  leaves  were  buried. 
Later,  soil  from  under  the  plants  where  the  leaves  were  buried 
was  sprayed  with  water  onto  plants  in  the  greenhouse  and  a  few 
infection  spots  appeared.  These  experiments  seem  to  confirm 
our  field  observations  that  the  spattering  rains  carry  infection 
from  the  soil  to  the  leaves. 

Spread  of  Disease  in  Marked  Fields.  In  order  to  determine 
the  spread  of  wildfire  under  ordinary  field  conditions,  six  fields 
were  selected  that  were  set  out  by  growers  with  plants  from  seed- 
beds having  no,  a  little,  and  considerable  wildfire.  These  included 
all  four  varieties  of  tobacco  grown  in  Connecticut.  On  the  first 
examination  or  two,  up  to  July  4th  before  there  was  any  field 
spread,  these  infected  plants  were  marked  by  numbered  labels 
stuck  in  the  ground  by  them.  After  the  spread,  note  was  merely 
taken  of  total  infected  plants  and  severity  of  attack.  It  was 
thought  that  by  marking  the  infected  plants  at  first  it  could  be 
seen  whether  or  not  subsequent  infections  clustered  around  these, 
but  the  spread  when  it  did  occur  was  usually  so  rapid  and  general 
that  no  special  centers  of  distribution  were  noticed.  Details  of 
these  fields  and  their  inspections  are  given  in  the  following 
paragraphs  and  Table  VI. 

Field  1,  Windsor.  This  was  Havana  tobacco  planted  with  seed- 
lings obtained  from  Portland,  where  there  was  no  wildfire  in  the 
seedbeds  or  anywhere  near  them.  Care  was  used  not  to  infect 
them  in  any  way  during  transportation  and  planting.  They  were 
put  out  in  a  low,  somewhat  wet  and  isolated  field  that  at  least 
had  never  had  any  serious  outbreak  of  wildfire.  Inspection  of 
Table  VI  shows  that  this  field  remained  entirely  free  of  infec- 
tion until  July  5th  and  that  no  general  spread  occurred  later.  Just 
after  the  first  spread,  examination  showed  on  July  5th  only  seven 
infected  plants  in  the  field,— five  of  these  had  only  a  single  spot 
on  a  leaf,  and  the  other  two  had  several  spotted  leaves.  These 
latter  appeared  as  if  infected  when  set  out  and  they  might  have 
served  as  the  source  of  infection  for  the  others.  They  were  pulled 
up  and  all  the  other  infected  leaves  were  removed.  The  second 
examination  on  July  21  showed  only  five  additional  infected  leaves, 


FIELD   EXPERIMENTS.  405 

four  with  two  or  three  infected  spots  and  one  with  ten.  Most  of 
these  leaves  were  in  the  vicinity  of  the  moderately  infected  plants 
previously  pulled  up.  Priming  was  begun  soon  after  so  no  further 
data  were  obtained  but  no  injury  resulted.  This  and  Field  2 
showed  the  value  of  setting  with  wildfire-free  seedlings. 

Field  2.  Rainbow.  This  was  a  Round  Tip  field  set  with  plants 
from  a  wildfire-free  bed.  No  wildfire  showed  on  the  inspected 
plants  at  any  of  the  four  examinations  made  from  June  20  to 
August  3d.  As  this  field  was  near  infected  seedbeds  that  had  been 
destroyed  after  it  was  planted,  its  freedom  from  wildfire  indicates 
that  the  disease  is  not  commonly  carried  any  distance.  The 
grower,  however,  was  careful  about  the  disease  getting  a  start, 
as  he  did  not  use  any  of  his  own  plants.  In  other  rows  in  the 
same  field  with  our  plot  and  on  Havana  tobacco  near-by,  a  few 
wildfire  spots  finally  appeared. 

Field  3,  East  Granby.  In  this  case  the  infected  Cuban  plants 
were  marked  under  a  tent.  These  came  from  the  grower's  seed- 
beds that  showed  considerable  wildfire,  but  care  was  used  to  avoid 
infected  plants  as  much  as  possible.  The  few  found  on  the  1st 
and  2d  examinations,  June  3  and  15,  were  all  seedbed  infections 
and  averaged,  on  the  last  date,  about  i/^%  for  the  marked  rows. 
The  next  examination  was  delayed  until  July  14,  at  which  time  the 
field  was  being  primed  the  first  time,  so  counts  could  not  be  made, 
but  it  was  evident  that  the  spread,  while  it  may  have  included 
more  plants,  was  so  light  on  these  that  no  very  evident  damage 
occurred,  and  the  subsequent  primings  would  keep  ahead  of  the 
trouble.     Injury  to  this  field,  apparently,  was  not  over  1%. 

Field  4,  Windsor.  Broadleaf  was  planted  in  this  field  from  a 
seedbed  that  showed  considerable  wildfire.  Inspections  on  June  3 
and  20  were  before  any  field  spread,  and  showed  on  the  last  elate 
about  6%  seedbed  infection.  After  the  first  spread  in  the  field  on 
July  6,  this  was  over  12%.  The  grower  after  the  second  inspec- 
tion removed  all  the  infected  leaves  from  the  experimental  plot, 
and  this  may  have  lessened  the  spread,  for  in  two  rows  in  which 
the  leaves  had  not  been  removed  counts  on  July  6  gave  51% 
infection.  This  field  was  not  followed  further  so  the  final  damage 
caused  was  not  determined.  The  infection  at  the  start,  however, 
was  abundant  enough  to  cause  serious  injury  judging  from  other 
similar  fields. 

Field  5,  Windsor.  The  field  was  set  with  Havana  plants  men- 
tioned under  seedbed  spraying  test  No.  4,  so  there  was  a  moderate 
amount  of  infection  to  start  with.  The  rows  selected  happened 
to  have  less  than  other  parts  of  the  field,  and  our  first  inspection 
of  June  20  revealed  no  infection  whatever.  It  was  quite  probable 
if  these  plants  had  been  examined  earlier,  soon  after  they  were 
set  out,  some  infected  leaves  would  have  been  found  that  later 
disappeared  and   so   gave  a   false  impression  of   freedom   from 


406  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

disease.  After  the  first  spread,  counts  on  July  5  showed  10% 
of  these  plants  infected.  This  was  not  nearly  so  high  as  in  other 
parts  of  the  field  and  the  amount  per  plant  was  not  so  serious. 
The  grower  started  in  priming  about  the  middle  of  July  so  no 
counts  were  made  on  the  next  inspections.  For  this  particular 
part  of  the  field  the  disease  was  kept  in  check  by  the  priming  and 
weather  so  that  probably  less  than  5%  injury  resulted. 

Field  6,  Sufneld.  This  Havana  field  certainly  had  a  good  chance 
for  injury  as  it  was  set  from  the  grower's  badly  diseased  seedbeds 
with  no  particular  care  to  avoid  wildfire  plants.  As  a  result  of 
our  first  count  on  June  3,  we  found  that  the  average  infection 
for  the  two  marked  plots  was  36%  and  twelve  days  later,  before 
any  spread,  this  increased  to  42%  because  of  the  masked  seedbed 
infections  developing.  On  July  8  after  the  first  field  spread,  it 
had  reached  90%  and  of  course  was  very  bad  on  some  of  the 
plants.  One  of  the  plots  was  protected  from  the  wind  by  a  barn 
and  also  happened  to  get  fewer  infected  plants  to  start  with,  31% 
as  compared  with  69%,  so  the  final  damage  here  was  much  less 
than  in  the  other  plot  at  the  further  side  of  the  field.  We  esti- 
mated the  total  damage  to  the  field  to  be  about  20%.  and  if  it 
had  not  been  harvested  early,  just  before  the  second  infection 
period  (the  last  of  July),  this  would  have  been  considerably 
greater.  As  it  was,  counts  made  on  July  8th  in  the  badly  infected 
plot  showed  23%  of  the  plants  badly  injured,  41%  moderately, 
34c/c  slightly,  and  only  2%  free  from  wildfire. 


Table  VI.     Infection  in  Marked  Fields  at  Different  Dates. 

Condition    Total  Plants        No.  Inf.  Plants  on  Examinations 
Field.     Locality.      Variety.  Seedlings.       Marked.         1st.       2d.  3d.  4th. 

1       Windsor,        Havana,   Free, 


2  Rainbow,  R.  Tip,  Free, 

3  E.  Granby,  Cuban,  Mod., 

4  Windsor,  Broad!.,  Consid., 

5  Windsor,  Havana,  Mod., 

6  Suffield,  Havana,  Bad, 


4294              07              10  Priming; 

Je.  20  Jl.    5        Jl.  21  no  injury. 

2000              000  0 

Je.  20  Je.  28       Jl.    s  Aug.    3 

6030             75         84      Priming;  Priming; 

Je.    3  Je.  15       Jl.  14  no  damage. 

iQ/8            51        104          242  No  later 

Je.    3  Je.  20       Jl.    6  data. 

1733              0         183     Priming.  Plowed  up. 

Je.  20  Jl.    5        Jl.  21  Aug.    3 

733            265       310           656  Cut 

Je.    3  Je.  15       Jl.    8  Jl.  26 


Removal  of  Infected  Leaves.  These  plants,  Jones'  experimental 
plots  with  crosses,  were  set  out  June  4th  at  the  Windsor  tobacco 
farm.  The  plants  came  from  a  seedbed  in  which  wildfire 
developed  conspicuously,  and  the  plants  were  kept  moist  in  baskets 
for  one  or  two  days  before  planting ;  wildfire  was  very  evident 
soon  after  they  started  to  grow.     There  were  four  rows  in  each 


FIELD    EXPERIMENTS. 


407 


plot.  On  June  20  the  first  counts  were  made  and  all  infected 
leaves  removed  from  rows  1-2  of  each  plot.  On  July  6  counts 
were  again  made  and  all  infected  leaves  again  removed  from  row 
1  of  each  plot.  Unfortunately  counts  were  never  made  of  infected 
plants  and  leaves  in  rows  3-4  and  of  rows  1-2  after  July  6th. 
However,  observations  made  at  this  date  and  later  showed  little 
difference  in  apparent  infection  between  the  plants  in  the  rows  in 
which  the  leaves  were  never  removed  and  those  that  had  been 
removed  once  and  twice.  In  fact  the  first  count  showed  infected 
plants  (see  Table  VII)  in  row  1  of  the  different  plots  ranging 
from  15%  to  81%,  and  yet  on  the  second  count  the  least  infected 
rows  had  just  as  high  a  percent,  of  infection  as  the  others,  the 
range  for  all  being  only  97%  to  100%.  The  first  removal  average 
from  1.8  to  5.2  leaves  per  infected  plant  for  the  different  plots 
and  the  second  from  4.1  to  5.4  leaves. 

That  the  first  removal  had  little  result  in  stopping  later  infec- 
tion is  shown  by  the  great  number  of  leaves  removed  in  each  case 
at  the  second  removal.  No  harm  was  done  by  the  first  removal, 
but  the  second  one  took  off  leaves  of  which  50%  were  of  commer- 
cial value.  This  removal  also  showed  in  somewhat  lessened 
growth  of  the  plants  subsequently.  The  second  removal  was  made 
after  the  first  spread  of  the  disease  in  early  July ;  if  it  had  been 
made  before  this,  say  about  June  27,  less  harm  to  the  plants  and 
more  effect  on  the  spread  of  the  wildfire  might  have  resulted. 
Again  the  plants  with  the  leaves  removed  were  so  close  to  those 
that  did  not  have  the  leaves  removed,  that  re-infection  from  them 
was  easy  and  so  may  have  nullified  the  effect  of  their  removal.  As 
an  experiment  under  the  conditions  which  it  was  tried,  it  did  not 
show  any  favorable  result  from  the  removal  of  the  infected  leaves. 


Table 

VII. 

Removal  of  Infected  Leaves  from  Field  Tobacco. 

No.  ini 

.  leaves 

Total 

1st  removal. 

2d  removal. 

%  Inf.  plants. 

per  inf 

.  plants. 

'lot 

.  Row. 

plants. 

Inf.pl. 

Inf.  lvs. 

Inf.  pi. 

Inf.  lvs. 

1st  tm. 

2dtm. 

1st  tm. 

2dtm. 

I 

1 
2 

150 

121 
109 

254 
191 

146 

603 

81 

97 

2.1 
1.8 

4.1 

2 

5 
6 

155 

113 
00 

288 
260 

152 

676 

73 

98 

2.6 
2.9 

4-4 

3 

9 
10 

162 

139 
95 

324 
253 

161 

759 

86 

99 

2.3 

2.8 

4-7 

4 

13 

160 

106 

292 

159 

826 

66 

99 

2.8 

5-2 

14 

122 

325 

2.7 

5 

17 

18 

142 

74 

186 

197 

142 

589 

52 

100 

2.5 
2.1 

4.1 

6 

21 
22 

itf 

110 

95 

315 
290 

152 

733 

7i 

97 

2.9 
3-1 

4.8 

7 

25 
26 

170 

30 

48 

98 
145 

170 

877 

18 

100 

3-3 
3-0 

5-2 

8 

29 
30 

164 

25 
38 

129 

155 

161 

864 

15 

98 

5-2 

41 

5-4 

408         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Fertiliser  Experiments.  These  rather  simple  fertilizer  tests 
were  made  on  the  infected  seedling  plots  1-6  at  the  Station's  Wind- 
sor tobacco  farm.  The  field  had  already  been  given  what  growers 
would  consider  a  rather  moderate  amount  of  fertilizer,  consisting 
of  one  application  of  Olds  &  Whipple's  tobacco  manure  at  the 
rate  of  a  ton  per  acre.  It  was  decided  to  divide  the  field  into  three 
strips  running  crosswise  of  the  plots.  The  first  thirty-eight  feet 
received  nitrate  of  soda  at  the  rate  of  250  lbs.  per  acre ;  the  second 
got  sulphate  of  potash  at  the  same  rate ;  while  the  third  and  larg- 
est strip  received  no  further  fertilization.  The  plants  at  this  time, 
July  12,  had  grown  considerably.  No  counts  were  made  as  other 
factors  entered  into  the  problem ;  for  example,  the  greater  protec- 
tion against  wind,  etc.,  of  the  plants  at  the  further  end  of  the  field 
which  received  no  further  fertilization.  However,  it  was  evident 
that  the  first  or  nitrate  of  soda  strip  made  the  best  growth,  and 
had  the  most  wildfire.  The  sulphate  of  potash  strip  also  made  a 
fair  growth,  somewhat  less  than  the  nitrate  of  soda,  and  had  less 
wildfire.  The  check  was  the  poorest  in  growth  and  had  the  least 
wildfire ;  this  plot,  however,  would  not  have  been  considered 
sufficiently  fertilized.  Just  how  much  was  due  to  poor  fertilization 
and  consequent  slow  hardy  growth  of  the  tobacco,  and  how  much 
to  the  greater  wind  protection,  in  the  limiting  of  wildfire  spread 
in  the  check,  could  not  be  determined. 

Spraying  Field  Plants.  These  experiments  were  conducted  on 
plants  at  the  Station's  Windsor  tobacco  farm.  Plants  in  plots  1-6 
already  mentioned  were  used  in  part.  The  last  ten  plants  in  rows 
2  to  46,  making  450  plants  in  all,  were  sprayed  five  different  times 
with  homemade,  4-4-50,  Bordeaux  mixture,  without  lead  arsenate, 
on  the  following  dates  :  June  20,  June  28,  July  6,  July  14,  July  26. 
These  plants  had  been  set  out  on  June  7,  and  included  plants  both 
badly  diseased  and  practically  free  from  wildfire.  It  happened 
that  the  end  of  the  field  sprayed  was  the  end  in  which  wildfire  did 
not  spread  so  rapidly  or  extensively  as  the  opposite  end,  but  this 
makes  no  difference  between  the  sprayed  and  unsprayed  plants 
compared  here. 

In  order  to  determine  the  effect  of  the  spraying,  the  sprayed 
plants  in  two  rows  of  each  plot  (except  plot  1  with  one  row)  were 
compared  on  July  27  with  the  same  number  of  unsprayed  plants 
in  the  same  rows  and  next  to  them.  This  count  was  just  before 
the  first  priming  and  at  a  time  when  wildfire  had  completed  its 
spread  from  the  first  infections  of  early  July.  The  details  are 
given  in  Table  VIII.  This  shows  that  in  every  case  the  sprayed 
plots"  had  fewer  infected  plants,  leaves  and  spots  than  the  corre- 
sponding unsprayed  plots.  There  had,  however,  been  much  less 
spread  in  the  sprayed  and  unsprayed  wildfire- free  or  nearly  free 
plants  than  on  those  that  were  badly  infected  when  set  out. 

The  average  of  the  totals  showed  that  the  unsprayed  had  one 


FIELD   EXPERIMENTS.  409 

and  a  half  times  as  many  infected  plants,  two  and  a  half  times  as 
many  infected  leaves  and  over  eight  times  as  many  wildfire  spots 
as  the  sprayed  plants.  A  plant  was  called  infected  if  only  a  single 
wildfire  spot  showed  on  it,  so  the  true  value  of  the  control  by  spray- 
ing is  shown  by  the  number  of  spots.  It  must  be  remembered,  too, 
that  some  infections  on  the  sprayed  plants  were  there  before  spray- 
ing began. 

A  second  fact  shown  in  the  table  is  that  most  of  the  infections 
on  the  sprayed  plants  were  on  the  end  of  the  rows  next  to  the 
infected  unsprayed  plants  (see  end  of  Table  VIII),  as  the  near  end 
had  17  as  compared  to  15  infected  plants  at  the  further  end,  and 
almost  twice  as  many  infected  leaves,  and  three  times  as  many  wild- 
fire spots.  This  indicates  that  had  the  sprayed  plants  been  entirely 
isolated  there  would  have  been  even  fewer  infections.  Where 
wildfire  was  bad  on  the  plant  to  start  with,  the  beneficial  effect  from 
the  spraying  was  more  marked  than  where  there  was  little,  for  the 
unsprayed  plants  on  the  former  developed  over  eight  times  as  many 
spots  as  on  the  sprayed,  while  the  latter  only  six  times  as  many. 


4IO         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 


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LABORATORY    STUDIES.  411 


Laboratory  Studies. 


Cultures.  Cultures  of  Bacterium  tabacum  are  obtained  fairly 
easily  from  the  wildfire  spots  on  tobacco  leaves.  The  method 
finally  used  by  us  was  to  soak  small  pieces  of  the  infected  leaf  tissue 
for  about  one  minute  in  corrosive  sublimate  solution,  i  to  1,000. 
After  washing  these  in  sterilized  water,  they  were  crushed  with  a 
sterilized  scalpel  in  a  test  tube  containing  about  5  c.c.  sterilized 
beef  broth.  This  was  sometimes  allowed  to  incubate  for  an  hour  or 
more,  after  which  one  to  three  drops  were  introduced  into  a  test 
tube  of  melted  beef-peptone  agar,  which,  after  thorough  shaking, 
was  poured  into  a  Petri  dish.  From  the  resulting  isolated  colo- 
nies, pure  cultures  were  eventually  obtained.  Practically  all  cul- 
tures were  grown  at  room  temperature  without  the  use  of  an  incu- 
bator. A  variation  of  this  method,  used  in  the  beginning,  consisted 
of  grinding  the  tissue  with  a  few  c.c.  of  water  in  a  mortar  with 
sand,  all  of  which  had  been  sterilized.  About  three  drops  of  the 
liquid  were  smeared  over  the  surface  of  hardened  agar  in  a  Petri 
dish.     See  Plate  XXXII  c-d. 

Attempts  to  obtain  cultures  from  old  dried  leaves  and  from  seeds 
were  tried  in  several  cases,  but  it  was  difficult  to  isolate  the  germ, 
even  when  it  was  known  to  be  present.  Finally  from  one  of  the 
old  dried  leaf  tissue  nine  months  old,  cultures  were  obtained,  but 
not  from  the  other  leaves  or  seeds.  This  may  have  been  due 
to  over-sterilization  or  to  faulty  technique,  since  the  same  crushed 
unsterilized  tissues  when  applied  in  moisture  directly  to  pricked 
leaves  often  gave  quite  successful  inoculations. 

In  general,  no  effort  was  made  to  distinguish  between  the  dead 
center  and  the  living  yellow  halo  of  the  spots  in  obtaining  cultures. 
However,  to  satisfy  ourselves  that  bacteria  were  not  confined  either 
to  the  dead  spots  or  to  the  yellow  halo  surrounding  them,  material 
was  selected  several  times  from  each  of  these  restricted  areas  and 
it  was  equally  easy  to  obtain  the  germ  from  either  region.  No 
attempts  were  made  to  isolate  the  germ  from  seed-pods  or  ribs 
of  the  leaves.  We  have  no  doubt,  however,  that  the  germ  can  be 
isolated  from  either  when  infected. 

Considerable  variation  existed  in  the  virulence  of  the  germ 
obtained  in  pure  culture,  depending  upon  the  age  of  the  same.  In 
general,  young,  recently  inoculated  cultures  were  more  virulent 
than  those  several  months  old  that  had  been  frequently  renewed. 
An  old  culture  received  from  Wolf  also  seemed  to  have  lost  its 
virulence.  However,  on  Dec.  30th  we  made  successful  inoculations 
with  a  culture  that  had  not  been  renewed  since  June  6th.  In  this 
particular  case  the  culture  had  been  kept  at  room  temperature  and 
had  been  dried  out  for  some  time,  but  before  using  it  was  soaked 
in  water  for  several  hours.  The  manner  in  which  the  inoculation 
is  made  is  also  an  important  factor  of  its  success,  a  subject  which 
will  be  discussed  later. 


412         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

The  Organism.  The  germ  is  readily  stained  with  gentian  violet, 
fudisin,  etc.,  but  these  alone  do  not  bring  out  the  flagella.  After 
trying  several  methods,  our  best  results  were  with  Moore's  modifi- 
cation of  Loeffler's  stain.  Our  description  of  the  bacteria  are  based 
chiefly  on  slides  stained  in  this  manner. 

In  common  with  most  bacteria  it  is  difficult  to  distinguish  this 
species  entirely  by  its  morphology.  Its  pathogenicity  to  tobacco 
is  its  striking  characteristic.  There  are,  however,  certain  dis- 
crepancies in  the  characters  assigned  to  it  by  Wolf  and  Foster  (32.) 
and  those  observed  by  us.  For  this  reason  a  brief  discussion  of 
it  here  is  desirable. 

The  size  of  the  organism,  as  stated  by  them,  varies  "from  2.4 
to  5  by  0.9  to  1.51U,,  the  most  common  size  being  3.3  by  i.2/a." 
According  to  our  measurements,  we  find  it  varying  from  1.3  to 
2.5^  in  length  by  0.6  to  0.8/t  in  width.  Slagg  (24,  p.  25.)  obtained 
measurements  which  agree  very  well  with  our  own,  since  he  gives 
the  length  as  varying  from  1.4  to  2.8/x  and  the  width  from  0.5  to 
0.75/x.  The  largest  size  described  by  Wolf  and  Foster  may  have 
been  due  to  measuring,  as  one,  individuals  which  had  not  been 
completely  divided.  In  our  stained  slides  the  bacteria  are  fre- 
quently seen  in  pairs  in  various  stages  of  division,  and  in  measur- 
ing these  one  is  sometimes  uncertain  whether  to  consider  them  as  a 
single  or  two  germs.  The  measurements  we  have  given  here  are 
limited  to  those  of  isolated  individuals.  In  general,  the  germs 
are  short  rods  with  rounded  ends,  about  two  or  three  times  as  long 
as  broad.     See  Plate  XXXII  a. 

Wolf  and  Foster  distinctly  say  that  these  bacteria  have  one  polar 
flagellum.  Slagg,  on  the  other  hand,  states  that  the  germ  isolated 
by  him  from  Kentucky  and  Connecticut  had  from  three  to  six 
polar  flagella.  We  have  found  from  one  to  four  flagella,  with  one 
or  two  doubtful  cases  where  there  may  have  been  five.  Most  of 
the  bacteria  seen  by  us  had  one  or  two  flagella.  Counts  of  several 
hundred  show  about  the  following  proportion :  40%  with  one  fla- 
gellum, 45%  with  two  flagella,  13%  with  three,  and  2%  with  four. 
The  number  of  flagella  found,  however,  seems  to  us  to  depend 
somewhat  upon  the  success  that  attended  their  staining.  Where 
only  one  is  found,  one  cannot  be  sure  but  that  others  may  have  been 
broken  off,  especially  if  a  single  flagellum  comes  off  at  an  angle 
to  the  polar  end.  Very  frequently  one  finds  detached  fragments 
of  the  flagella  on  the  slide  and  the  varying  length  of  those  attached 
indicates  that  portions  have  been  broken  off.  On  one  of  our  slides 
the  appearance  of  the  rather  stiff,  coarse  flagella,  commonly  one 
at  a  pole,  suggested  that  they  might  have  been  accidentally  coa- 
lesced in  the  manipulations.  That  this  does  occur  is  shown  by 
frequent  individuals,  in  certain  slides,  where  a  branching  effect 
is  produced  by  the  flagella  coalescing  for  a  greater  or  less  extent 
and  then  separating  into  two  or  more.     A  forked  or  pronged  effect 


LABORATORY    STUDIES.  4X3 

is  thus  frequently  given.  In  general,  the  flagella  seem  to  be  two  or 
three  times  the  length  of  the  bacterium,  though  shorter  ones  were 
obtained  which  were  probably  broken  off.     See  Plate  XXXII  b. 

In  this  connection,  it  might  be  well  to  consider  the  characteristics 
of  Bacterium  angulatum  as  given  by  Fromme  and  Murray  ( Journ. 
Agr.  Res.  16:  225.).  In  table  form  they  mention  five  points  that 
distinguish  this  germ  from  Bacterium  tabacum.  Three  of  these 
relate  to  the  manner  of  liquifying  gelatine,  acid  formation  with 
saccharose,  dextrose,  etc.,  and  growth  in  the  closed  arms  of  fer- 
mentation tubes.  These  seem  to  be  chiefly  differences  of  degree 
rather  than  of  kind  and  so  cannot  be  considered  of  as  great 
importance  as  the  other  two  which  relate  to  size  of  the  germ  and 
number  of  flagella.  They  state  that  Bacterium  angulatum  varies 
from  2  to  2.5^  in  length  and  is  0.5/x  wide.  Contrasted  with  Wolf 
and  Foster's  measurements  of  Bacterium  tabacum  these  measure- 
ments are  distinct  but  vary  little  from  those  found  by  Slagg  and  us 
for  the  latter  germ.  They  give  the  number  of  flagella  as  varying 
from  three  to  six.  This  also  is  quite  different  from  the  single 
flagellum  mentioned  by  Wolf  and  Foster,  but  agrees  fairly  well 
with  the  number  found  by  us,  and  exactly  with  the  number  given 
by  Slagg  for  Bacterium  tabacum. 

From  the  preceding  considerations  it  will  be  seen  that  the  mor- 
phological differences  between  Bacterium  angulatum,  angular 
leaf  spot,  and  Bacterium  tabacum,  wildfire,  are  not  so  marked  as 
originally  considered  by  Fromme  and  Murray.  This  may  account 
for  the  confusion  of  the  tobacco  bacterial  spot  from  Africa,  men- 
tioned by  Klerck  (19),  where  the  spots  are  said  to  resemble  those 
of  wildfire  while  the  germ  agrees  with  the  angular  leaf  spot  organ- 
ism. Undoubtedly  a  comparative  study  of  the  two  germs  and  their 
effects  on  their  host  from  different  regions  of  the  world  is  needed 
to  bring  out  their  real  differences. 

Methods  of  Inoculation.  Altogether  several  hundred  infection 
experiments  were  tried  with  the  wildfire  germ  on  tobacco.  These 
were  mostly  under  greenhouse  conditions ;  some,  however,  were 
carried  on  outdoors  under  varying  natural  conditions.  In  the 
greenhouse,  inoculations  were  made  at  all  times  of  the  year. 
According  to  the  environmental  conditions  and  the  manner  of 
inoculation,  different  results  were  obtained.  The  former  we  will 
consider  later.  The  latter  may  be  described  briefly  here  as  follows  : 
(1)  The  first  method  tried  consisted  merely  of  placing  pure 
cultures  of  the  germs,  or  the  crushed  tissues  containing  them,  in 
a  moderate  amount  of  water  and  pouring  it  over  the  leaves  to  be 
infected.  A  variation  of  this  method  consisted  in  dropping  with  a 
medicine  dropper  the  water  containing  the  germs  on  the  host.  This 
method  proved  the  least  satisfactory  of  any  of  those  tried.  It  was 
most  successful  when  the  conditions  for  natural  infections  outdoors 
were  present.     It  was  not  so  effective  in  the  greenhouse  unless 


414  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

those  conditions  were  simulated.  However,  it  was  very  satisfac- 
tory when  the  tissues  to  be  infected  were  injured  so  that  the  germs 
could  gain  entrance  through  the  injured  places.  The  injury  was 
usually  accomplished  by  pricking  the  tissues  with  a  sterilized  needle. 
Unless  the  environmental  conditions  were  unusually  favorable  the 
infections  almost  always  were  limited  to  these  pricked  spots.  This 
was  especially  true  in  our  winter  experiments.     See  Plate  XXX  b. 

(2)  The  second  method  employed  was  to  spray  pure  cultures 
of  the  germ  in  water  on  the  plants  by  means  of  an  atomizer.  This 
was  very  successful  outdoors  when  natural  conditions  were  just 
right.  In  the  greenhouse,  it  was  most  successful  when  accom- 
panied by  needle  pricks  in  the  tissues,  as  noted  before.  The 
disadvantages  of  this  very  successful  method  lies  in  the  fact  that 
the  atomizer  has  to  be  thoroughly  sterilized  each  time  after  a 
culture  from  a  different  source  is  used. 

(3)  This  method  consisted  of  pricking  the  tissues  in  definite 
places  with  a  needle  which,  after  being  sterilized,  had  been  intro- 
duced into  a  pure  culture.  The  advantage  of  this  method,  which 
is  also  almost  always  successful,  is  due  largely  to  infection  taking 
place  only  at  definitely  marked  points. 

In  any  of  these  methods  efforts  were  made  to  keep  the  plants 
under  favorable  moist  conditions  for  a  few  hours  after  the  inocula- 
tion. This  was  done  in  part  by  spraying  with  water,  placing  them 
under  a  bell  jar  or  in  a  shady  position,  or  by  making  the  inocula- 
tions on  a  cloudy  or  moist  day. 

Relation  to  Environment.  As  has  already  been  shown  in  this 
paper,  environmental  factors  are  very  important  in  determining  the 
spread  of  the  disease  in  nature.  The  same  holds  true  in  relation  to 
artificial  infection,  especially  when  no  puncturing"  or  injuring 
of  the  tissues  is  provided  for  entrance  of  the  germ.  The  two 
factors  of  most  importance  are  favorable  moisture  conditions  and 
rapid  growth  of  the  host.  In  the  greenhouse  experiments,  espe- 
cially during  the  winter,  these  two  factors  did  not  always  occur,  and 
especially  with  the  very  slow  growing  plants  infections  were  limited 
unless  the  tissues  were  punctured. 

To  secure  more  favorable  conditions,  the  plants,  some  time  pre- 
vious to  inoculation,  were  frequently  placed  under  bell  jars  to  facili- 
tate the  opening  of  the  stomates,  thus  favoring  the  entrance  of 
the  germs.  Likewise  in  the  heat  of  early  summer  a  cheese-cloth 
tent  was  built  on  the  ground  in  the  greenhouse  to  shade  the  plants 
and  to  retain  a  more  moist  atmosphere. 

It  might  be  stated  here  that  the  greenhouse  conditions  under 
which  we  worked  were  such  that  there  was  little  or  no  accidental 
infection.  Very  little  care  was  needed  to  keep  the  check  plants 
isolated  from  the  infected  ones  on  this  account,  especially  in  the 
cooler  months.  This  failure  to  spread  will  not  hold  true  in  nature 
where,  under  certain  conditions,  the  disease  spreads  rapidly  from 


LABORATORY    STUDIES.  41.5 

infected  to  free  plants.  These  differences  are  well  illustrated  by 
the  following  experience.  A  number  of  small  plants  in  the  green- 
house were  artificially  inoculated  without  puncturing,  only  a  few 
spots  appearing  on  all  of  them.  The  plants  were  kept  for  some 
time  under  these  conditions  with  no  spread  whatever  of  the  infec- 
tion, although  they  were  frequently  sprinkled.  Later  the  plants 
were  taken  out  of  the  crocks  and  transplanted  in  an  isolated  place 
outdoors.  They  began  to  grow  more  rapidly,  and  when  a  moist, 
favorable  period  arrived  the  wildfire  spread  suddenly  and  abun- 
dantly all  over  the  newer  leaves. 

Relation  to  Host.  Although  in  the  greenhouse  experiments  we 
were  most  successful  with  those  inoculations  where  the  tissues  were 
punctured,  there  is  no  doubt  in  our  minds  that  in  nature,  where 
the  disease  suddenly  spreads  under  favorable  environment,  the 
infections  usually  take  place  through  the  uninjured  tissues.  This 
undoubtedly  occurs  by  the  passage  of  the  motile  germs  through  the 
open  stomates.  Examination  of  the  tobacco  leaves  shows  that  the 
stomates  are  abundant  on  both  the  upper  and  lower  surfaces, 
although  somewhat  more  numerous  on  the  lower.  Under  favorable 
environmental  conditions  for  the  opening  of  the  stomates,  both 
outdoors  and  in  the  greenhouse,  we  were  able  to  produce  abundant 
infections  on  the  uninjured  tissues  by  applying  the  germs  alone 
either  to  the  upper  or  lower  surface  of  the  mature  or  nearly 
mature  leaves.  However,  when  they  were  sprayed  over  the  imma- 
ture leaves  rarely  did  infection  occur.  Similar  freedom  from  infec- 
tion of  young  leaves  is  seen  in  nature  and  indicates  that  entrance 
takes  place  through  the  stomates,  which  in  these  leaves  are  not  so 
fully  developed  or  liable  to  be  open.  Furthermore,  that  it  was  a 
question  of  open  stomates  and  not  of  the  age  of  the  tissues,  is 
shown  by  the  fact  that  young  leaves  are  very  easily  infected  after 
puncturing. 

This  last  statement  leads  us  to  a  consideration  of  the  age  of 
the  tissues  in  reference  to  their  susceptibility  to  artificial  infection. 
In  several  cases  we  tried  comparative  tests  in  inoculating  over-ripe 
and  somewhat  yellowing  leaves,  with  those  in  their  prime  and  the 
young  or  immature  leaves,  all  on  the  same  plant.  Where  the  punc- 
turing method  was  used  we  found  that  the  young  leaves  apparently 
show  the  most  successful  infections,  especially  by  sharper  contrast 
of  the  halo  spots  with  the  normal  tissues,  and  possibly  by  their 
larger  size.  This  contrast  was  nearly  as  evident  on  the' leaves 
in  their  prime,  but  much  less  so  on  the  older  over-ripe  leaves. 
On  the  latter,  especially  when  yellowed,  the  infections  were  fre- 
quently not  very  evident,  and  as  the  general  yellowing  progressed 
they  become  entirely  obscured.  To  our  minds,  this  is  explained  by 
the  fact  that  young  leaves  have  more  food  for  growth,  and  as  the 
chlorophyll  granules  are  the  parts  more  directly  attacked,  leaves  in 
their  prime  furnish  a  more  favorable  environment  than  do  the 
old  yellowing  leaves. 


416         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

Tissues  Invaded.  When  we  employed  the  puncturing  method  of 
inoculation  we  found  it  equally  easy  to  secure  infections  in  the  leaf 
parenchyma,  ribs,  or  the  stems  of  growing  greenhouse  plants.  No 
attempts  were  made  to  inoculate  the  floral  parts  or  seed-pods. 
Certain  differences  showed  in  the  results  of  infection  at  these  three 
different  points  of  inoculation.  For  example,  in  the  leaf  blades, 
round  yellow  halo  spots  that  eventually  reached  a  diameter  of  one- 
half  inch  or  so  were  the  common  result.  In  time,  as  the  spots 
reached  their  maximum  size,  dead  centers  of  more  or  less  extent 
appeared,  but  these  were  not  so  common  or  quick  to  develop  as  with 
natural  infections  outdoors. 

If  these  inoculations  were  made  on  the  veins,  nearly  similar 
results  were  obtained.  When,  however,  the  inoculations  were 
made  on  the  midrib,  yellowing  was  more  extended  in  a  linear 
direction  up  and  down  either  side  of  the  same  and  less  definitely 
marked  off  from  the  surrounding  healthy  green  tissues.  Likewise 
some  of  the  yellowing  extended  out  along  the  lateral  divergent 
ribs.  Soon  dead  spots  appeared  in  the  tissues  parallel  to  the 
midrib,  and  frequently  smaller  ones  along  the  lateral  ribs.  This 
indicates  more  of  an  up  and  down  spread,  as  if  the  germ  or  its 
toxin  followed  the  course  of  the  veins.  It  made  little  difference 
whether  the  midrib  was  inoculated  near  its  apex  or  its  base,  as  the 
disease  seems  to  spread  as  readily  downward  as  upward.  Plate 
XXX  c. 

Where  the  young  stems  were  inoculated  below,  but  away  from 
the  base  of  the  leaf,  an  elongated  blackening  of  the  tissues 
occurred  in  the  vicinity  of  the  puncture.  In  time  the  leaf  immedi- 
ately above  showed  yellowing  and  spotting,  somewhat  similar  to 
that  described  for  the  inoculations  of  the  midrib.  In  some  cases 
upper  leaves  away  from  the  point  of  inoculation  showed  a  slight 
yellowing  of  the  leaf  blade  in  the  vicinity  of  the  midrib.  Whether 
this  yellowing  had  anything  to  do  with  the  immediate  presence  of 
the  germs,  or  was  merely  a  secondary  result,  we  did  not  determine. 
A  single  attempt  to  inoculate  plants  with  such  leaves  was  unsuc- 
cessful. Neither  did  we  try  to  determine,  by  inoculation  tests  or 
staining,  the  presence  of  the  germs  widespread  in  stems  or  the 
midribs.  In  the  parenchyma,  however,  both  in  the  dead  centers 
and  yellow  halo  spots,  the  presence  of  the  germs  was  demonstrated 
both  by  staining  and  by  inoculations  with  tissues  from  these 
restricted  regions. 

Methods  of  Survival.  Cotton  Seed  Meal.  We  have  already 
mentioned  our  failure  to  secure  infection  of  tobacco  plants  by 
means  of  cotton  seed  meal.  In  these  tests  eighty-one  samples  of- 
cotton  seed  meal,  recently  collected  over  the  State  by  the  Station's 
sampling  agent,  were  used  on  greenhouse  plants  in  the  spring  of 
1921.  A  small  amount  of  each  fertilizer  was  soaked  for  a  short 
time  in  water  and  then  sprinkled  over  a  small  tobacco  plant  in  a 


LABORATORY    STUDIES.  4J7 

crock.  It  is  to  be  regretted  that  no  punctures  were  made  in  the 
leaves  of  the  plants  to  secure  more  certain  infection  if  the  germs 
were  present.  However,  other  plants  similarly  sprinkled  with 
germs  in  water  at  the  same  time  of  year  were  successfully  inocu- 
lated. These  results  seem  to  indicate  that  this  fertilizer  is  not  a 
means  by  which  the  germs  are  carried  over  from  one  year  to 
another.  This  is  the  only  fertilizer,  except  tobacco  stems,  in  which 
it  is  at  all  likely  that  the  germs  could  be  carried  from  the  south. 

Tobacco  Stems.  Similar  experiments  were  tried  in  a  few  cases 
with  commercial  tobacco  stems,  such  as  are  used  in  field  fertiliza- 
tion, but  of  unknown  origin,  and  of  leaves  and  stems  of  wildfire 
tobacco  overwintered  in  a  barn.  No  results  were  obtained  from 
any  of  these.  The  barn-cured  wildfire  tobacco  when  first  used 
was  about  a  year  old  and  the  inoculated  plants  were  unpunctured. 
This  may  account  for  our  failure  to  secure  successful  infection 
from  it,  since  we  later  secured  successful  infection  from  dried 
herbarium  wildfire  leaves  equally  old  when  the  puncturing  method 
was  used.  This  barn  wildfire  tobacco  was  used  again  on  punc- 
tured leaves,  when  it  was  a  year  and  a  half  old,  but  no  successful 
inoculations  resulted.  We  believe,  however,  with  this  method  we 
could  secure  successful  inoculations  with  barn-cured  wildfire 
tobacco  that  is  not  over  a  year  old. 

Dried  Herbarium  Leaves.  In  the  winter  of  1922  we  attempted 
to  isolate  the  germ  from  dried,  herbarium,  wildfire,  tobacco  leaves 
of  varying  ages.  We  were  unsuccessful  in  all  of  these  except  two. 
Both  were  from  seedling  tobacco  leaves  from  the  same  source 
collected  early  in  May,  1921,  and  the  cultures  were  isolated  in  Feb- 
ruary, 1922,  over  nine  months  later.  Successful  inoculations  were 
made  with  the  isolated  germ.  Failure  to  isolate  this  germ  from 
the  other  sources  was  not  due  to  death,  but  rather  to  the  presence 
of  other  germs  and  lack  of  sufficient  attempts  to  secure  it.  This 
was  proved  by  the  later  successful  inoculation  of  pricked  leaves 
with  these  crushed  herbarium  leaves  soaked  in  water.  By  this 
method  infections  were  obtained  from  this  dried  material  in  twenty 
out  of  twenty-seven  attempts.  The  leaves  were  from  thirteen 
different  sources,  eight  of  which  were  tried  successfully  from  one 
to  three  times,  and  one  tried  successfully  twice  and  unsuccessfully 
once,  while  four  were  tried  unsuccessfully  one  or  two  times.  Four 
other  inoculations  were  made  with  a  mixture  of  tissues  from  two  to 
four  of  these  sources,  but  each  limited  to  the  dampening  off,  the 
halo  or  the  dead  center  stage,  all  of  which  were  successful. 

The  material  used  was  obtained  from  both  seedbed  and  field 
plants  of  several  varieties  of  1921  tobacco.  All  but  two  were 
from  material  collected  in  the  State,  one  from  Vermont  and  the 
other  from  Florida.  We  secured  infections  with  the  Vermont,  but 
not  with  the  Florida  material.  Only  one  attempt,  however,  was 
made  with  the  latter.     The  leaves  in  the  various  experiments  had 


418         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

been  dried  from  198  to  298  days  when  used  for  inoculation. 
Success  was  had  with  the  oldest,  as  well  as  with  the  youngest. 
There  was  considerable  variation  in  the  vigor  of  development  of 
the  infection  spots,  even  on  the  same  plant.  Material  from  differ- 
ent sources  also  seemed  to  show  variation  in  vigor.  These  experi- 
ments prove  that  the  germs  can  retain  their  viability,  at  least  for 
a  considerable  period,  in  dried  material  that  has  not  been  exposed 
to  the  elements.  There  is  no  question,  therefore,  that  refuse  from 
barn-cured  wildfire  tobacco  is  a  menace  if  used  on  land  planted 
with  tobacco  the  following  year. 

A  single  one  of  these  experiments  will  suffice  to  illustrate  the 
average  results  obtained,  using  Infection  Numbers  2042  and  3003 : 
The  leaves  were  gathered  from  a  wildfire  field  at  Somers,  Conn., 
Aug.  26,  192 1,  and  separate  inoculations  were  made  Mar.  7  and 
Mar.  17,  1922.  Both  were  successful.  In  the  first,  three  leaves 
on  each  plant  were  pricked  with  a  needle  about  eight  times  before 
the  water  containing  the  crushed  infected  tissues  was  poured  over 
them.  Inoculation  2042  was  made  on  three  plants  and  about  a 
week  later  showed  five,  nine  and  sixteen  fair  to  good  infection 
spots  at  the  punctured  places.  One  infection  spot  appeared  at  an 
unpunctured  place,  which  was  very  unusual  in  these  experiments. 
Inoculation  3003  was  made  on  a  single  plant  with  an  indefinite 
number  of  pricks  in  the  three  leaves.  An  examination  ten  days 
later  showed  seven  good  and  eight  fair  infection  spots  on  two  of  the 
leaves  and  none  on  the  third. 

Later  similar  infection  experiments  were  tried  with  older  dried 
herbarium  wildfire  leaves  collected  in  1920.  These  experiments 
were  made  in  late  April,  1922.  The  leaves  had  been  dried  in  these 
cases  from  573  to  651  days  when  crushed  and  placed  in  water  on 
the  plants.  They  were  from  twelve  different  fields  in  Connecticut. 
In  none  of  these  did  any  of  the  inoculations  take.  This  seems 
to  indicate  that  the  germs  can  not  retain  their  vitality  much  over 
a  year  in  the  old  dried  leaves. 

Seed.  We  were  unsuccessful  in  six  attempts  to  isolate  the 
wildfire  germ  from  supposedly  infected  1920  Round  Tip  tobacco 
seed,  these  being  made  one  or  two  years  after  it  was  gathered. 
We  also  failed  to  secure  infection  from  water  in  which  the  same 
seed  had  been  soaked  several  hours.  Several  months  previously 
the  same  seed  planted  in  the  greenhouse  had  given  one  infected 
seedling  and  we  have  reason  for  believing  that  it  was  the  source 
of  infection  in  several  seedbeds  in  1921. 

We  artificially  infected  unsterilized  tobacco  seed  with  the  wild- 
fire germ  but  in  the  one  or  two  attempts  to  re-isolate  it  we  also 
failed  because  of  the  presence  of  other  bacteria.  However,  one 
month  after  the  seed  was  inoculated  infections  were  secured  when 
it  was  soaked  in  water  and  this  was  applied  to  punctured  plants. 
The  same  seed  several  days  after  inoculation  was  placed  outdoors, 


LABORATORY    STUDIES.  4X9 

protected  from  the  rain  but  exposed  to  the  cold,  from  Feb.  14  to 
April  18.  On  the  latter  date  part  of  it  was  soaked  in  water  several 
days  and  then  applied  to  punctured  plants  which  later  showed  a 
few  infections.  About  two  weeks  later  the  experiment  was 
repeated  with  even  better  results.  These  experiments,  while  not 
entirely  satisfactory,  indicated  on  the  whole  that  the  germ  may 
retain  its  viability  on  tobacco  seed  for  some  months. 

Overwintered  Refuse.  We  have  tried  several  times  to  infect 
punctured  greenhouse  plants  with  infected  refuse  from  tobacco 
plants  that  had  overwintered  in  the  field.  Badly  disintegrated 
leaves,  from  the  Station  garden  plot  already  mentioned,  were 
gathered  at  different  times.  These  were  ground  up  further  and 
soaked  from  one  hour  to  several  days  in  water.  This  water  with 
some  fragments  of  the  tissue  was  poured  over  needle-punctured 
plants.  Altogether  twenty-seven  plants  were  thus  inoculated  and 
on  these  we  succeeded  in  securing  three  poor  and  three  fair  to 
good  infection  spots.  These  experiments  indicate  that  the  germs, 
to  a  certain  extent,  can  be  wintered  over  in  infected  leaves  left 
outdoors  in  the  field  and  undoubtedly  under  favorable  conditions 
are  the  source  of  occasional  infections  the  succeeding  year.  From 
our  experience  this  is  not  a  great  menace  in  the  field,  but  should 
be  a  warning  to  the  grower  not  to  leave  tobacco  refuse  in  the  seed- 
beds after  the  plants  have  been  pulled.  This  overwintering  is  also 
shown  somewhat  by  the  following  experiment.  On  Feb.  1st  arti- 
ficially infected  plants  were  changed  from  a  warm  to  a  cold  green- 
house and  on  March  1st  placed  outdoors.  They  were  thus  exposed 
for  some  time  to  freezing  weather.  The  soaked  crushed  infected 
tissues  from  these  gave  vigorious  infections  on  punctured  green- 
house plants  late  in  April. 

Soil.  We  have  already  mentioned  the  experiment  where  infected 
leaves  were  buried  in  the  soil  under  disease  free  plants  which 
later  became  infected,  and  the  successful  inoculations  made  with 
the  same  soil  a  month  or  two  later  after  the  leaves  had  become 
entirely  disintegrated.  This  showed  that  the  germs  could  be 
carried  in  the  soil  for  a  short  period. 

We  have  further  data  that  indicate  that  they  may  be  carried  over 
the  winter  in  this  manner  at  least  to  a  limited  extent.  Samples 
of  soil  on  different  occasions  in  March  and  April  were  taken  from 
the  Station  garden  plot  which  the  previous  year  had  grown  wild- 
fire plants  that  had  been  allowed  to  rot  in  place.  After  sifting  off 
the  coarse  particles  of  soil  the  fine  particles  were  soaked  in  water 
for  several  hours  and  applied  to  pricked  tobacco  plants  in  the  • 
greenhouse.  The  first  experiment  with  six  plants  produced  no 
results.  In  the  second  experiment  with  three  plants,  each  pro- 
duced a  single  fair  to  good  infection  spot.  Of  course  these  germs 
may  have  come  from  the  very  finely  disintegrated  tobacco  tissues 
rather  than  from  germs  entirely  free  in  the  soil,  but  the  general 
statement  that  they  carry  over  in  the  soil  is  approximately  correct 


420         CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

since  it  is  difficult  to  distinguish  between  the  mineral  part  and 
the  fine  humus  of  the  soil. 

In  a  tobacco  seedbed,  however,  on  which  pure  cultures  of  the 
wildfire  germ  were  sprayed  in  the  fall,  we  failed  to  secure  infection 
of  plants  the  next  spring  by  spraying  on  pricked  leaves  water  in 
which  this  soil  was  soaked. 

Infection  of  Sprayed  Plants.  Our  field  experiments  showed 
that  seedlings  and  field  plants  sprayed  with  Bordeaux  mixture  were 
partially  or  entirely  protected  from  infection  according  to  the  num- 
ber and  efficiency  of  the  treatments.  This  was  also  tested  out 
with  artificial  infections  in  the  greenhouse  and  similar  results  were 
obtained.  On  several  occasions  pricked  plants  were  inoculated  by 
atomizing  with  the  germ  as  follows:  1,  Check  plants  inoculated 
but  no  other  treatment ;  2,  Plants  sprayed  with  Bordeaux  mixture 
immediately  before  inoculation ;  3,  Plants  sprayed  with  Bordeaux 
mixture  immediately  after  inoculation;  4,  Plants  sprayed  with 
Bordeaux  mixture  immediately  before  and  after  inoculation.  In 
the  latter  case  infection  never  took  place  unless  the  puncture  was 
at  a  point  poorly  protected  by  the  spray.  Where  the  plants  were 
sprayed  either  before  or  after  inoculation  there  was  only  an  occa- 
sional infection.  On  the  unsprayed  plants  infection  took  place 
at  practically  all  the  punctured  spots. 

Infection  with  African  Material.  We  were  very  successful  in 
making  infections  with  wildfire  tobacco  leaves  received  from  Miss 
Doidge,  collected  in  Rustenburg,  Transvaal,  Jan.  2,  1922.  These 
inoculations  were  made  in  both  April  and  May,  1922,  and  were 
equally  successful  in  both  cases,  infection  appearing  at  most  of  the 
many  pricked  places  on  which  the  water  containing  the  crushed 
infected  tissues  was  applied.  These  infections  were  typical  and 
fully  as  virulent  as  inoculation  from  our  own  cultures  made  at 
the  same  time. 

Infection  of  Other  Hosts.  In  nature  we  have  never  seen  wild- 
fire on  any  of  the  weeds  or  cultivated  plants  in  or  adjoining  the 
seedbeds  or  tobacco  fields.  Our  experiments  to  infect  other  hosts 
at  first  were  limited  to  the  tomato  and  a  cultivated  species  of  flower- 
ing tobacco.  In  neither  were  the  leaves  pricked  before  inoculating 
and  this  may  account  for  the  failure  in  both  cases.  Later  inocula- 
tions on  pricked  leaves  of  young  plants  of  tomato,  pepper,  egg- 
plant, jimson  weed  and  poke  weed  were  tried.  Three  plants  were 
used  in  each  case  and  each  had  from  thirty  to  fifty  pricked  places. 
Apparently  all  of  these  failed  of  infection,  except  possibly  the 
pepper  and  the  eggplant.  On  the  former  three  or  four  and  on 
the  latter  one  slight  faint  yellowish  spots  appeared  at  punctured 
places.  These  possible  infections,  however,  were  quite  indefinite 
as  compared  with  those  that  appeared  in  the  tobacco  plants  sim- 
ilarly inoculated  at  the  same  time. 

Wolf  and  Foster  (32,  p.  452.)  originally  claimed  to  have  inocu- 


RECOMMENDATIONS    FOR    CONTROL.  42 1 

lated  tobacco  with  wildfire  obtained  from  cowpeas.  In  a  later 
publication,  however,  Wolf  and  Moss  (33,  p.  32.)  state  that  "all 
efforts  to  prove  that  the  wildfire  organism  is  parasitic  in  plants 
other  than  tobacco  have  thus  far  failed."  These  inoculated  plants 
included  potatoes,  tomatoes,  peppers,  eggplants,  jimson  weed  and 
horse  nettle,  all  of  which  are  related  to  tobacco.  Chapman  and 
Anderson  (2,  p.  74.)  succeeded  in  inoculating  "petunia,  egg- 
plant and  pokeweed  (Phytolacca  dccandra)  by  spraying  with 
suspensions  of  bacteria  in  water  in  the  same  way  in  which  tobacco 
plants  were  usually  inoculated.  Some  of  the  leaves  in  each  case 
were  wounded  by  puncture  with  a  sterile  needle."  They  also 
isolated  the  germ  from  spots  on  tomatoes  growing  in  an  infected 
tobacco  seedbed. 

Recommendations  for  Control. 

Seedbeds.  (1)  If  wildfire  developed  at  all  in  the  beds  the  pre- 
vious year,  either  make  beds  on  new  land  away  from  all  possible 
sources  of  infection,  or  sterilize  the  old  beds  and  paths  with  steam 
heat.  Heat  the  soil  for  20  to  30  minutes  at  a  pressure  of  at  least 
100  lbs.  Boards,  sash  and  cloth  used  on  beds  or  fields  previously 
infected  should  be  thoroughly  sprinkled  all  over  with  formalin, 
1  to  25  parts  of  water,  and  piled  in  a  dry  place  to  slowly  dry  off ; 
or  the  cloth  can  be  heated  in  boiling  water  for  one  hour. 

(2)  Use  seed  known  to  have  come  from  a  wildfire-free  field  and 
which  has  been  protected  at  all  times  from  subsequent  contamina- 
tion. If  in  doubt  place  seed  in  a  cheesecloth  bag  in  a  jar  and  soak 
for  10  to  15  minutes  in  a  corrosive  sublimate  solution,  rate  of  1 
part  of  corrosive  sublimate  [Poison  !]  to  1,000  parts  water.  Then 
wash  thoroughly  with  pure  water  and  dry  immediately. 

(3)  Use  as  little  water  on  plants  as  is  consistent  with  good 
growth  and  apply  at  such  times  as  it  will  most  quickly  dry  off  the 
leaves  without  sun-scorch  injury.  Air  the  beds  when  feasible  both 
day  and  night,  and  especially  in  moist  weather,  in  the  best  possible 
ways  to  prevent  water  of  transpiration  settling  on  the  leaves. 

(4)  No  matter  what  the  previous  treatment,  as  a  final  precau- 
tion spray  the  plants  with  Bordeaux  mixture ;  if  homemade  use 
the  4-4-50,  or  if  commercial  as  recommended  on  package.  Begin 
treatment  on  the  very  young  seedlings  soon  after  roots  start  and 
largest  leaves  are  the  size  of  a  finger-nail,  and  repeat  spraying  each 
week  until  the  season  for  pulling  is  over.  Clean  up  seedbeds  at 
end  of  setting  and  plant  beds  with  a  different  crop  if  desired. 

Fields.  (1)  In  setting  out  the  fields  use  only  plants  known  to 
come  from  the  wildfire-free  seedbeds.  If  impossible  to  get  these, 
select  only  the  plants  apparently  free  of  the  disease  and  from  parts 
of  the  beds  least  infected.  Plant  as  soon  as  pulled  and  keep  water 
off  the  leaves  while  in  the  baskets. 

(2)  About  a  week  after  setting  out  plants  go  over  the  field  and 
remove  diseased  plants,   and   if   possible  make   a   second  similar 


42  2  CONNECTICUT    EXPERIMENT    STATION    BULLETIN    239. 

inspection  about  a  week  or  ten  days  later.     Take  plants  pulled  up 
off  the  field.     Reset  with  healthy  plants. 

(3)  In  case  these  inspections  show  the  field  badly  infected, 
plow  it  up  and  reset  with  healthy  plants,  providing  this  can  be  done 
in  time  to  insure  the  newly  set  field  properly  maturing  before 
danger  from  frosts. 

(4)  In  some  cases,  especially  where  the  tobacco  is  primed,  it 
may  be  preferable,  instead  of  resetting  or  doing  nothing,  to  go  over 
the  field  once  or  twice  and  remove  the  infected  and  non-commercial 
lower  leaves.  These  also  should  be  taken  off  the  field,  instead  of 
being  thrown  on  the  ground.  The  first  removal  should  be  made 
about  a  week  after  planting  and  the  second  after  the  plants  have 
started  to  grow. 

LITERATURE. 

Most  of  the  following  papers  have  been  referred  to  in  the  preceding" 
discussions.  They  include  practically  all  of  the  literature  relating  to 
wildfire.  Some  of  them  are  merely  brief  notes  on  the  presence  of  the 
disease  in  certain  localities. 

r.  Chapman,  G.  H.  Tobacco  Wildfire.  Mass.  Agr.  Coll.  Extens. 
Serv.  Circ.  82:    1-7.     D.  1920. 

2.  Chapman,  G.  H.  and  Anderson,  P.  J.  Tobacco  Wildfire.  Pre- 
liminary Report  of  Investigations.  Mass.  Agr.  Exp.  Sta.  Bull. 
203:   67-81.     S.  1921. 

3.  Chapman,  Garner,  Valleau.  Wildfire  caused  by  Bacterium 
tabacum.  U.  S.  Bur.  PI.  Ind.  PI.  Dis.  Bull.  PL  Dis.  Surv.  4:  79. 
15  S.  1920. 

4.  Clayton,  Clinton,  O  strain,  Valleau.  Wildfire  caused  by  Bacterium 
tabacum.  U.  S.  Bur.  PI.  Ind.  PL  Dis.  Bull.  PL  Dis.  Surv.  5:  19-20. 
Jl.  1921. 

5.  Clinton,  G.  P.  Wild  Fire  of  Tobacco  in  Connecticut.  U.  S.  Bur. 
PL  Ind.  PL  Dis.  Surv.  Letter.     12  My.  1921. 

6.  Fromme,  F.  D.  Wildfire  and  Angular  Spot.  Virg.  Agr.  &  Mech. 
Coll.  Extens.  Div.  Bull.  62:    25-31.     Je.  1920. 

7.  Fromme,  F.  D.  Wildfire  caused  by  Bacterium  tabacum.  U.  S. 
Bur.  PL  Ind.  PL  Dis.  Bull.  PL  Dis.  Surv.  5:    37.     15  JL  1921. 

8.  Fromme,  F.  D.  Seed  Treatment  for  Tobacco.  Virg.  Polyt. 
Instit.  Manifold  Copy  3250:    1-3.      ?D.  1921. 

9.  Fromme,  F.  D.  and  Wingard,  S.  A.  Treatment  of  Tobacco  seed 
and  suggested  program  for  control  of  wildfire  and  angular-spot. 
Amer.  Phytop.  Soc.  Abstracts  1920:    21.     D.  1920. 

10.  Foster,  Fromme,  Ludwig.  Wildfire  caused  by  Bacterium  taba- 
cum. U.  S.  Bur.  PL  Ind.  PL  Dis.  Bull.  PL  Dis.  Surv.  5:  65.  Au. 
1921. 

11.  Garner,  W.  W.  Observations  on  Tobacco  Wildfire.  Hartford 
Co.  Farm  News.  4:    5.     Je.  1921. 

12.  Haskell,  R.  J.  and  Wood,  J.  I.  Wildfire  caused  by  Bacterium 
tabacum,  Wolf  &  Foster.  U.  S.  Bur.  PL  Ind.  PL  Dis.  Bull.  PL 
Dis.  Surv.  Suppl.  16:   268.     Je.  1921. 

13-     Hesler,  Johnson.     Wildfire  caused  by  Bacterium  tabacum.     U.  S. 

Bur.  PL  Ind.  PL  Dis.  Bull.  PL  Dis.  Surv.  4:    98.     O.  1920. 
14.     Jenkins,  E.  H.     Wildfire  of  Tobacco.     Conn.  Agr.  Exp.  Sta.  Bull. 

Im.  Inf.  12:    1-2.     D.  1920. 


i6 


LITERATURE.  423 

15.     Jenkins,  E.  H.     Warning  to  Tobacco  Growers.     Conn.  Agr.  Exp. 

Sta.  Bull.  Im.  Inf.  15:    1-2.     My.  1921. 

Jenkins,   E.  H.   and  Chapman,   G.   H.     Condensed   Recommenda- 
tions for  the  Control  of  Wildfire.     Conn.  Agr.  Exp.  Sta.     Tobacco 

Exp.  Sta.  Bull,  r:    1-4.     J  a.  1922. 
17.     Johnson,  J.     Status  of  tobacco  diseases.     U.  S.  Bur.  PI.  Ind.  PL 

Dis.  Bull.  PI.  Dis.  Surv.  4:   99.     O.  1920. 
iS.     Johnson,  J.     The  Relation  of  Air  Temperature  to   certain   Plant 

Diseases.      The    "Wildfire"    leaf   spot    of   Tobacco.      Phytop.    11: 

455-6.     N.  1921. 
19.     Klerck,  G.W.  (editor).     Departmental  Activities.     Botany.     Journ. 

Dep.  Agr.  Union  S.  Afr.  2:   210.     Mr.  1921.     Ibid.  2:  310.     Ap.  1921. 

Ibid.  4:    117.     F.  1922. 
20      Orton,  C.  R.     Wildfire  caused  by  Bacterium  tabacum.     U.  S.  Bur. 

PI.  Ind.  PI.  Dis.  Bull.  PI.  Dis.  Surv.  5:    37-     Jl.  1921. 
21.     Osmun,  Clinton,  Valleau.     Wildfire  caused  by  Bacterium  tabacum. 

U.  S.  Bur.  PI.  Ind.  PL  Dis.  Bull.  PI.  Dis.  Surv.  5:    106.     S.  1921. 

Reinking,   O.     Philippine    Plant   Diseases.     Phytop.   9:     130.     Mr. 

1919. 

Shamel,   A.   D.     The    Selection   of  Tobacco   Seed   Plants.     Conn. 

Agr.  Exp.  Sta.  Bull.  150:    I-I3-     Je.  i9<>5- 

24.  Slagg,  C.  M.  Preliminary  report  on  a  study  of  the  wildfire  dis- 
ease of  tobacco.  Amer.  Phytop.  Soc.  Abstracts  1921:  25-6.  D. 
1921. 

25.  Southwick,  B.  G.  Tobacco  Wildfire  does  serious  Damage.  Hart- 
ford Co.  Farm  News  4:   2.     My.  1921. 

26.  Thomas,  R.  C.  On  the  Control  of  Wildfire  and  Angular-Spot 
Diseases  of  Tobacco.  Virg.  Polyt.  Inst.  Ext.  Div.  New  3:  3-  Mr. 
1921. 

27.  Thurston,  Selby.  Wildfire  caused  by  Bacterium  tabacum.  U.  S. 
Bur.  PI.  Ind.  PI.  Dis.  Bull.  PI.  Dis.  Surv.  5:    88.     S.  1921. 

28.  Valleau,  W.  D.  Wildfire  caused  by  Bacterium  tabacum.  U.  S. 
Bur.  PI.  Ind.  PI.  Dis.  Bull.  PI.  Dis.  Surv.  4:    52.     Au.  1920. 

29.  Westbrook,  E.  C.  In  letter  to  Fromme.  U.  S.  Bur.  PI.  Ind.  PI. 
Dis.  Bull.  Suppl.  16:   268.     Je.  1921. 

30.  Wolf,  F.  A.  Tobacco  Wildfire.  N.  Car.  St.  Coll.  Agr.  Ext.  Serv. 
Circ.  61:    r-4.     Mr.  1918. 

31.  Wolf,  F.  A.  and  Foster,  A.  C.  Bacterial  Leaf  Spot  of  Tobacco. 
Science  n.  s.  46:    361-2.     O.  1917. 

32.  Wolf,  F.  A.  and  Foster,  A.  C.  Tobacco  Wildfire.  Journ.  Agi. 
Res.  12:   449-58.     F.  1918. 

33.  Wolf,  F.  A.  and  Moss,  E.  G.  Diseases  of  Flue-Cured  Tobacco 
with  Suggestions  for  Application  of  Palliative,  Preventive  and 
Remedial  Measures. — Wildfire.  The  Bull.  N.  Car.  Dept.  Agr.  40: 
24-34.     D.  1919- 

34.  Evans,  I.  B.  P.  Tobacco  Wildfire  {Bacterium  tabacum).  Journ. 
Dep.  Agr.  Union  S.  Afr.  4:    57.     Ja.  1922. 


p 


PLATE  XXIX. 


Types  of  Tobacco  Seedbeds. 


a.     Glass  Sash,  p.  383.  b.     Cloth  Covers,  p.  383. 

Wildfire  Plants  Killed  with  Formalin. 


c.     Isolated  Spots,  p.  401.  d.     Whole  Beds,  p.  401. 

First  or  Dampening-off  Stage. 


e.     Dead    Spot,   p.  380.  f.     Infected    Leaves,    p.    380. 

WILDFIRE  IN  SEECBEDS. 


PLATE  XXX. 


Natural  Infections. 


a.     Leaves   from   Seedbed,  p.  381. 
Artificial  Infections. 


b.     In  Leafblade,  p.  414.  c.     In  Midrib,  p.  416. 

SECOND  OR  HALO  STAGE  OF  WILDFIRE. 


PLATE  XXXI. 


Individual  Leaves. 


a.     Second  or  Halo  Stage,  p.  387.  b.     Third  or  Sunscorch  Stage,  p.  387. 

Broadleaf  Plants. 


c.     This   Field  almost  completely   Ruined,  p.   387. 
WILDFIRE  IN   FIELD   PLANTS. 


PLATE  XXXII. 


Photomicrographs  of  the  Germ. 


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a.     Many  Germs,  p.  412 
x  500  diam. 


b.     Showing  Flagella, 
x  1500  diam. 


p.  413. 


Artificial  Cultures. 


c.     In    Test-tube,   p.   411.  d.     In  Petri  Dish,  p.  411. 

THE   GERM  OF  WILDFIRE. 


Q  Q  R  1  h 

J  ,J  O  O  -t 


University  of 
Connecticut 

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